ABSTRACT

With the advances of technology, security of the digital media has become a major challenge.

One way to ensure safety and control over the unauthorized distribution of the media is to

effectively hide some classified information in it so that the intellectual property rights of the

owner can be proved as and when required.

Watermarking is the technique to embed some data into the signal for identifying the copyright

ownership and preventing piracy. By pre-processing the image watermark and hiding it in a

carrier stream, a robust watermarking technique is presented, resisting all the signal processing

manipulations and deliberate attacks. In digital watermarking, the signal may be audio, pictures,

or video. If the signal is copied, then the information also is carried in the copy. A signal may

carry several different watermarks at the same time.

Digital watermarking is a technology that opens a new door for authors, producers, publishers

and service providers for protection of their rights and interest in multimedia documents.

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CHAPTER 1

Introduction

With the rapid growth of Internet, it is easier for digital data owners to transit multimedia files

across the Internet. Thus, there is a huge increase in concentration overcopyright protection of

media. Traditionally, encryption and control access techniques were used to protect the

intellectual property rights. These techniques do not protect against unauthorized copying after

the media have been successfully transmitted and decrypted.

Cryptography guarantees confidentiality, authenticity, and integrity when a message is

transmitted across the network. It does not protect against unauthorized copying after

successful message transmission. Watermarking is an efficient way to protect copyright of

media. Watermarking is a technique of embedding a special pattern, watermark, into a

multimedia document so that a given piece of copyright information is permanently tied to the

data. This information can later prove the ownership, identify a misappropriating person, trace

the marked documents dissemination through the network, or simply inform users about the

rights-holder or the permitted use of the data.

Motivation

The technological advances have led to the multiple copying of digital media without incurring a

loss in quality. These unlimited copying causes a considerable loss to the copyright holders. To

enforce intellectual property rights and to restrain the unauthorized distribution of the media,

some information is hidden in it for proving the ownership. Hence, the main motivation for

taking watermarking as a research topic is to develop an effiective algorithm for embedding and

extraction of the hidden information (watermark) for data files. The goal in this project is to

embed the watermark in the audio signal imperceptibly by the exploitation of the statistical and

the objective properties of the cover signal. The low frequency region and the energy of the

signal segments are considered in this regard. Lastly, the robustness of the implemented strategy

is evaluated against signal processing and intentional attacks which mainly include the de-

synchronization attacks and this defines the final aim of the undertaken project.

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1.1 Objective

1. To develop an effective algorithm for embedding and extraction of the hidden information

(watermark) for files.

2. To embed watermark imperceptibly by exploiting the statistical and the objective properties.

3. To evaluate robustness of the implemented strategy against de-synchronization attacks.

1.2 Digital Watermarking

With the advancements in technology and increased access to the digital media, the copyright

protection of media has gained a lot of importance. To prevent piracy of media and its

unauthorized distribution, the owner or the creator of the media needs to prove his intellectual

property rights. This is where watermarking comes into picture. Watermarking is a strategy to

embed some classified information into the media perceptually or non-perceptually to prove the

ownership. Watermark is the data which is hidden into the digital media for proving the

intellectual property rights. The main properties of the watermark include:

1. Imperceptibility

2. Undetectability

3. Resistance to all signal manipulations

4. Extractability to prove ownership

5. Unambiguity

The watermark should be imperceptible in the manner that the changes made to cover object for

embedding the watermark should not create a very high order of distortion. That is the quality of

the cover object should remain unaffected despite the changes done in it for hiding the

watermark thereby, making the watermark imperceptible. The watermark should also be

undetectable when searched by any malicious user with an aim to destroy or remove it. Another

property that the watermark needs to exhibit is its resilience to the signal manipulations and other

deliberate attacks. It should be so embedded in the cover work that it is resistant to all changes

made in the cover work. Lastly, the watermark should be extractable to some acceptable extents

to prove the copyright ownership whenever required to do so. These attributes of the watermarks

have to be taken into account before developing the algorithm for its embedding and extraction.

Also, the watermark should be unambiguous so that no two parties may claim for the same

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media work. Watermark, when extracted, should be able to prove the copyright ownership most

efficiently.

1.3 Classification of Watermarking Techniques

The watermarking techniques used to embed information are dependent on the requirements of

the applications that the cover work is to be used for. So it is designed according to the type of

cover media, resilience to attacks and environment in which it is used. The taxonomy is shown in

figure 1. The division of the watermarking strategies has been done in following main streams on

the basis of:

1. Cover Media

2. Domain

3. Extraction strategy

4. Resistance to attacks

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Figure 1.1: Taxonomy of Watermarking Techniques

On the basis of cover media used: The watermarking algorithms are broadly classified into 5

categories depending on the cover work that is to be watermarked. These are:

1. Text

2. Image

3. Audio

4. Video

5. Software

In text watermarking algorithms, spacing between the letter, words and lines or the typing style

is manipulated in a manner to embed the watermark. The changes reflect the embedding of

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watermark in the document. Image watermarking scheme has been the most popular research

area in watermarking. Exhaustive research has been carried out in this direction. There are two

domains in which the watermarking is done namely:

1. Spatialdomain

2. frequency domain

In spatial domain, changes are made to the pixel values of the image in order to embed the

watermark which can be another image or any other signal. In frequency domain, transform is

applied to the image and then coefficients are changed to embed the watermark depending on the

frequency region in which the watermark needs to be hidden. This embedding of watermark is

dependent on the Human Visual System (HVS).

Audio watermarking is another domain of work where the watermark is embedded in the audio

signal to curb the unlimited piracy of the media. Audio watermarking is comparatively difficult

to implement due to the sensitivity of the Human Auditory System. The modifications are made

to amplitude values of the samples or to the transform coefficients when any transform is applied

to the audio signal.

Video watermarking involves the embedding to be done in the continuous image frames of the

video or to the audio part of the signal or to both. Since, human auditory system is more sensitive

to changes in amplitude so the watermark embedding is carried out in the pixel values of image

frames. Software watermarking is done in order to discourage software piracy. Watermark can

be embedded in the code part or in the data of the software.

Watermark can be some classified textual information which when extracted can prove the

copyright ownership. On the basis of domain: The watermarking algorithms can be broadly

classified into two categories:

1. Time/ spatial domain

2. Frequency/ Transform domain

In spatial domain, the watermark is embedded by directly modifying the values of cover object.

For example, in images the pixel values can be modified and in audio the amplitude values can

be manipulated. In transform domain, a transform is applied to the cover object and then

manipulations are done to the transform coefficients in the required frequency band. The main

transforms in common use are: Discrete Cosine Transform (DCT), Discrete Fourier Transform

(DFT), Discrete Wavelet Transform (DWT) etc.

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On the basis of extraction strategy: This classification is done on the basis of the fact whether the

original cover object or some extra information is required for watermark extraction. It is divided

into three broad categories:

1. Non blind techniques

2. Semi blind techniques

3. Blind techniques

In the non blind strategy the original cover work is required to extract the watermark. The main

disadvantage of this method is that extra bandwidth is required to send the original cover work as

well along with the watermarked work. In semi blind strategy, some information derived from

the original cover work, not exactly the original media is required for extracting the watermark.

This information can be any data derived from the media file. In the blind strategy, no extra

information is required for the extraction of the watermark. In comparison to blind strategy, non

blind watermarking algorithms are more resistant to attacks On the basis of resistance to attacks:

In this category of classification, watermarking scheme is again classified into three types:

1. Fragile

2. Semi fragile

3. Robust

The watermarking strategies come under the category of being fragile when they cannot sustain

the signal manipulation and intentional attacks. Semi fragile techniques can sustain some attacks

but they also fail against some of them. Robust strategies are those which are resistant to all the

deliberate and non deliberate attacks. They are capable of sustaining most of the attacks. That is,

the watermark can be successfully extracted or detected even if the cover work is corrupted with

attacks.

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1.4 Digital watermarking life-cycle phases

Figure 1.2 : Digital watermarking life-cycle phases

General digital watermark life-cycle phases with embedding-, attacking-, and detection and

retrieval functions

The information to be embedded in a signal is called a digital watermark, although in some

contexts the phrase digital watermark means the difference between the watermarked signal and

the cover signal. The signal where the watermark is to be embedded is called the host signal. A

watermarking system is usually divided into three distinct steps, embedding, attack, and

detection. In embedding, an algorithm accepts the host and the data to be embedded, and

produces a watermarked signal.

Then the watermarked digital signal is transmitted or stored, usually transmitted to another

person. If this person makes a modification, this is called an attack. While the modification may

not be malicious, the term attack arises from copyright protection application, where pirates

attempt to remove the digital watermark through modification. There are many possible

modifications, for example, lossy compression of the data (in which resolution is diminished),

cropping an image or video, or intentionally adding noise.

Detection (often called extraction) is an algorithm which is applied to the attacked signal to

attempt to extract the watermark from it. If the signal was unmodified during transmission, then

the watermark still is present and it may be extracted. In robust digital watermarking

applications, the extraction algorithm should be able to produce the watermark correctly, even if

the modifications were strong. In fragile digital watermarking, the extraction algorithm should

fail if any change is made to the signal.

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1.5 Purpose of Digital Watermarking

Watermarks added to digital content serve a variety of purposes. The following list details six

purposes of digital watermarking (Memon & Wong, 1998).

Ownership Assertion – to establish ownership of the content (i.e. image)

Fingerprinting – to avoid unauthorized duplication and distribution of publicly available

multimedia content

Authentication and integrity verification – the authenticator is inseparably bound to the

content whereby the author has a unique key associated with the content and can verify integrity

of that content by extracting the watermark

Content labeling – bits embedded into the data that gives further information about the content

such as a graphic image with time and place information

Usage control – added to limit the number of copies created whereas the watermarks are

modified by the hardware and at some point would not create any more copies (i.e. DVD)

Content protection – content stamped with a visible watermark that is very difficult to remove

so that it can be publicly and freely distributed Unfortunately, there is not an universal

watermarking technique to satisfy all of these purposes (Memon & Wong, 1998). The content in

the environment that it will be used determines the digital watermarking technique. The

following section describes some digital watermarking techniques.

1.6 Properties

For better activeness, watermark should be perceptually invisible within host media, statistically

invisible to unauthorized removal, readily extracted by owner of image, robust to accidental and

intended signal distortion like filtering, compression, resampling, retouching, crapping etc. For a

digital watermark to be effective for ownership, it must be robust, recoverable from a document,

should provide the original information embedded reliably and also removed by authorized

users.

All these important properties of digital watermarks are described as-

1. Robustness :The watermark should be robust such that it must be difficult to remove. The

watermark should be robust to different attacks. The robustness describes whether watermark

can be reliably detected after performing some media operations.

2. Perceptual transparency:This property describes that whether watermark is visible or

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invisible to human sensor organ. Perceptible watermarks are visible to human while

imperceptible are not. Imperceptible watermarks are such that content remains same after

applying digital watermarking technique.

3. Security: Security property describes that how easy to remove a watermark. This is generally

referred to as attack on watermarking. Attack refers to detection or modification of watermark.

4. Complexity: This is important property which is to be consider in real time applications like

video. Complexity property is concerned with amount of effort needed to extract or retrieve the

watermark from content.

5. Capacity : Capacity property of digital watermarks refers to amount of information that can

be embedded within the content. The important point is that more data is used in watermark,

watermark will become less robust.

In addition to these properties, watermarks are having some extra properties as unambiguity,

tamper resistance, inseparable from the works and able to undergo some transformation as

works.

1.7 Why to use it?

First important application come into mind is copyright protection of digital media.It is easy to

duplicate digital data exactly without quality loss. Similar to process in which artist signed their

painting with a brush to claim their copyrights, artist of today can watermark their work and hide

some information say their name in the image. Hence, embedded watermark will allow to

identify the owner of work. This concept is applicable to digital video and audio also. Especially,

distribution of digital audio over internet in MP3 format is currently a big problem. Digital

watermarking may be useful to setup controlled audio distribution and provide efficient means

for copyright protection, usually in collaboration with international registration bodies such as

IDDN(Inter Deposite Digital Number). In addition with copyright protection, Digital

watermarking is playing a important role in many fields of applications such as broadcast

monitoring, owner identification, transaction tracking, proof of ownership, fingerprinting,

content authentification, copy control, device control. Digital watermarks can also serve as

invisible labels and content link. For example, photo development labs may insert a watermark

into the picture to link the print to its negative.so, it is becomes easy to find out negative of a

print. All one has to do is to scan the print and extract the information from negative. In a

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completely different scenario, the digital watermarks may be used as a geometrical reference

which may be useful for programs such as Optical Character Recognition(OCR) software. The

embedded calibration watermark may improve the detection reliability of the OCR software

since it allows the determination of translation, rotation and scaling. Digital watermarking also

serves as a means of advertising within the digital media. For instance, the user may download

and view a digital image, use a watermark reader to extract the digital signature, then access a

web based directory to find the company’s name and up-to-date address, phone number and web

and e-mail address. Digital watermarks also serves the purposes of identifying quality and

assuring authenticity. A graphic or audio file bearing digital watermark can inform the viewer or

listener who owns to the item.

The technique Digital Watermarking is the recent research in the field of multimedia and internet

copyright protection field. There are various applications of digital watermarking as broadcast

monitoring, owner identification, proof of ownership, transaction tracking,content authentication,

copy control, device control and so on. Out of these, some important applications are described

as-

1.Broadcast monitoring

This application identifies that when and where works are broadcast by recognizing watermarks

embedded in these works. There are variety of technologies to monitor playback of sound

recording on broadcast. The digital watermarking is alternative to these technologies due to it’s

reliable automated detection. A single PC based monitoring station can continuously monitor to

16 channels over 24 hours with no human interaction. Resulted monitoring is assembled at

central server and is now available to interested one .The system can distinguish between

identical versions of songs, which are watermarked for different distribution channel. Such

system requires Monitoring infrastructure and watermarks to be present in content.Watermarking

video or music is planned by all major entertainment componies possessing closed networks.

2. Encoding

According to the thinking of major music companies and major video studios, encoding happens

at mastering level of sound recording. In such downstream, transactional watermarks are also

considered. Each song is assigned with unique ID from the identifier database.After completion

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of all mastering processes, ID is encoded in sound recording.To enhance encoding of audio or

video recordings requiring special processing, the human-assisted watermark key is available.

3. Copy and playback control

The data carried out by watermark may contain information about copy and display permissions.

We can add a secure module into copy or playback equipment to automatically extract the

permission information and block further processing if required.This approach is being taken in

Digital Video Disc(DVD).

4. Content authentication

The content authentication is nothing but embedding the signal information in Content. This

signature then can be checked to verify that it has not been alter. By watermarks, digital

signatures can be embedded into the work and any modification to the work can be detected.

CHAPTER 2

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Image Watermarking

A watermark is A pattern of bits inserted into a digital image file that identifies the file's

copyright information (author, rights, etc.). The name “watermark” is derived from the faintly

visible marks imprinted on organisational stationery.

Unlike printed watermarks, which are intended to be somewhat visible (like the very light

compass stamp watermarking this report), digital watermarks are designed to be completely

invisible.

Figure2.1: Image watermarking

The purpose of digital watermarks is to provide copyright protection for intellectual property that

is in digital format.

As seen above, Alice creates an original image and watermarks it before passing it to Bob. If

Bob claims the image and sells copies to other people Alice can extract her watermark from the

image proving her copyright to it.

The caveat here is that Alice will only be able to prove her copyright of the image if Bob hasn’t

managed to modify the image such that the watermark is damaged enough to be undetectable or

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Image 1

Alice

watermark

Send to Bob

copies

Watermark Image

added his own watermark such that it is impossible to discover which watermark was embedded

first.

2.1 Technical Details

Digital watermarking technology makes use of the fact that the human eye has only a limited

ability to observe differences. Minor modifications in the colour values of an image are

subconsciously corrected by the eye, so that the observer does not notice any difference.

While vendors of digital watermarking schemes do not publicly release the exact methods used

to create their watermarks, they do admit to using the following basic procedure (with obvious

variations and additions by each vendor).

A secret key (string or integer) produces a random number which determines the particular

pixels, which will be protected by the watermarking. The watermark is embedded redundantly

over the whole image, so that every part of the image is protected.

Figure2.2 : Working

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One way of doing this is by “Patchwork”. This technique uses a random number generator to

select n pairs of pixels and slightly increases or decrease their luminosity (brightness level). Thus

the contrast of this set is increased without any change in the average luminosity of the image.

With suitable parameters, Patchwork even survives compression using JPEG.

Although the amount of secret information has no direct impact on the visual fidelity of the

image or the robustness of the watermark, it plays an important role in the security of the system.

The key space, that is the range of all possible values of the secret information, x must be large

enough to make exhaustive search attacks impossible.

In the process of extracting the watermark, the secret key is used to identify the manipulated

pixels and finally to decode the watermark.

As an example of poor engineering, an early version of Digimarc’s watermarking software gave

each licensed user an ID and a two-digitnumeric password, which were issued when she registers

with Digimarc and pays for a subscription.

The password checking mechanism could easily be removed by flipping a particular “flag” bit

and the passwords had only 99 possibilities so it was short enough to be found by trial and error.

A deeper examination of the image also allowed a villain to change the ID and thus the copyright

of an already marked image as well as the type of use (such as adult -> general public content).

Before embedding a mark, watermarking software usually checks whether there is already a

mark in the picture, but this check can be bypassed fairly easily with the result that it is possible

to overwrite any existing mark and replace it with another one.

The quality of digital watermarks can be judged in two ways; firstly it must be able to resist

intentional and unintentional attacks and secondly the embedded watermark must not detract

from the quality of the image.

The higher the resistance of a watermark against attacks, the higher the risk of the quality of the

image being reduced, and the greater the chance of obvious visual artefacts being created.

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2.2 Methods used to test Watermark Robustness

These are some of the methods that can be used to test whether a watermark can survive different

changes to the image it is embedded in.

Compare this Original Image with the attacked images below, and see if you can spot any

changes in quality.

Horizontal Flipping

Many images can be flipped horizontally without losing quality. Few watermarks survive

flipping, although resilience to flipping is easy to implement.

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Rotation & Cropping

A small rotation with cropping doesn’t reduce image quality, but can make watermarks

undetectable as rotation realigns horizontal features of an image used to check for the presence

of a watermark.

The example has been rotated 3 degrees to the right, and then had its edges cropped to make the

sides straight again.

JPEG Compression/Re-compression

JPEG is a widely used compression algorithms for images and any watermarking system should

be resilient to some degree to compression or change of compression level e.g. from 71% to 70%

in quality like the example .

Scaling

Uniform scaling increases/decreases an image by the same % rate in the horizontal and vertical

directions.

Non-uniform scaling like the example at left increases/decreases the image horizontally and

vertically at different % rates. Digital watermarking methods are often resilient only to uniform

scaling.

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Dithering

Dithering approximates colors not in the current palette by alternating two available similar

colors from pixel to pixel. If done correctly this method can completely obliterate a watermark,

however it can make an image appear to be “patchy” when the image is over-dithered (as in the

elbow area of the image).

Mosaic

A mosaic attack doesn’t damage the watermarked image or make it lose quality in any way, but

still enables the image to be viewed in eg: a web browser by chopping the image into subsections

of equal size and putting it back together again.

To the viewer a “mosaic” image appears to look the same as the original but a web crawler like

DigiMarc’s MarcSpider sees many separate images and doesn’t detect that these separate images

are parts of a watermarked image.

This means that the watermark cannot be detected, as a problem common to all image

watermarking schemes is that they have trouble embedding watermarks into small images, (less

than 256 pixels in height or width).

Stirmark

StirMark is the industry standard software used by researchers to automatically attempt to

remove watermarks created by Digimarc, SysCoP, JK_PGS (TALISMAN project – É.P.F.L.

algorithm), Signum Technologies and EIKONAmark.

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Stirmark attacks a given watermarked image using all the techniques mentioned in this report as

well as more esoteric techniques such as low pass filtering, gamma correction,

sharpening/unsharpening etc.

All vendors of digital watermarks have their products benchmarked by Stirmark and as of

August 2001, no watermark from any vendor survives the test, ie: the watermarks are all

removed without degradation to image quality occurring.

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Chapter 3

Audio Watermarking

With the development of the internet and increase in the need for the security and integrity of the

data in transit on the network, watermarking has gained a great interest. With this, the protection

of intellectual property rights has become one of the areas of main concern. The main work in

the field of watermarking has been focused on images and videos. Only a few audio

watermarking schemes have been reported till date. Digital audio watermarking is the scheme of

embedding some relevant information in the audio signal so as to prove the copy right

ownership. Audio watermarking is difficult to implement as compared to image watermarking

due to high sensitivity of human auditory system (HAS). The general strategy to implement

audio watemarking is diagrammatically given as:

Figure 3.1 : Audio Watermarking: General Strategy

The simplest visualization of requirements of the audio watermarking algorithms is the magic

triangle. Its vertices are inaudibility, robustness to attacks and watermark data rate. This triangle

is a perfect visual representation of the trade-offs between the watermark capacity and

robustness, keeping the perceptual quality of the watermarked audio at an acceptable level. It is

certainly not possible to attain high robustness and high watermark data rate simultaneously.

Hence, to achieve robustness against attacks,

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Figure 3.2 : Magic Triangle

capacity of the watermark has to be compromised. The requirements that have to be

satisfied among all the three are very much application dependent. As for an instance

in steganography applications, the algorithms have to attain robustness to attacks.

3.1 Human Auditory System

The Human Auditory System is very sensitive to slightest changes in the audio due to its wider

dynamic range. Hence watermarking of audio signals is more challenging as compared to

watermarking of images or video. The HAS perceives sounds over a range of power greater than

109:1 and a range of frequencies greater than103:1. The HAS is highly sensitive towards

Additive White Gaussian Noise (AWGN). The slight perturbations in a sound file are detected

even if they are as low as one part in ten million or 80dB below ambient level. This is because

the human ear can perceive amplitude distortion but it is relatively insensitive to phase distortion.

On the other hand, HAS has a fairly small differential range which means loud sounds can mask

out the weaker sounds .

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The human ear acts as a frequency analyser that maps signal frequencies to locations along the

basilar membrane. The HAS is generally modelled as a non uniform filter bank with

logarithmically widening bandwidth for higher frequencies. The bandwidth of each filter is set

according to the critical band, which is defined as the bandwidth in which subjective response

changes abruptly. Hence, HAS is modelled as a bandpass filterbank, containing strongly

overlapping bandpass filters with bandwidths around 100 Hz for bands with a central frequency

ranging between 500Hz to 5000 Hz for bands placed at high frequencies.

The main properties of the HAS mainly used in watermarking algorithms are frequency

(simultaneous) masking and temporal masking. Masking properties are exploited to embed

additional bit stream into the cover audio signal without generating the audible noise thus

keeping the watermark concealed.

3.2 Types of Audio Watermarking Techniques

Digital audio watermarking techniques can be broadly classiffied into 2 categories based

on the domain in which the watermarking is done:

1. Time domain

2. Frequency domain

Figure 3.4 : Taxonomy of Audio Watermarking Techniques

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In time domain audio watermarking schemes, the watermark is embedded by modifying the

audio signal itself. In transform domain, modifications are done on the transform coefficients of

the components of the audio signal. Time domain techniques can be further classified into two

categories (a) when the audio signal samples are modified for embedding the watermarking

(LSB Decoding method, Quantization method, phase watermarking method), (b) when inaudible

noise (watermark) is added on to the audio signal (addition of pseudo random sequence, echo

hiding method, patchwork method). The following sections will discuss various audio

watermarking techniques and the affect of various audio signal attacks on the robustness of the

watermark when embedded by these techniques.

3.2 Time Domain Techniques

When the watermark is directly embedded into the audio signal then they come under this

category and they are broadly classified into two parts on the basis of how the watermark is

embedded into the signal.

1. LSB Decoding Method

The simplest and most straight forward technique of embedding the watermark is to embed it

into the Least Significant Bits of the audio signal. Given the extraordinary high channel capacity

of using the entire audio signal for transmission, the watermark can be embedded into it multiple

number of times. The audio signal is first divided into segments and a subset of the segments is

selected. The LSBs of these segments are modified according to the bit of the watermark that is

to be embedded. Extraction of the watermark is performed by extracting the least significant bits

of the selected segments. If the extracted bits and the inserted bits match then the watermark is

successfully detected. It is a blind algorithm the original audio signal is not required for detection

of the watermark.

The advantages of this method are:

(a) As it is simple to implement, its algorithmic delay is very less.

(b) It has very high watermark capacity as stated earlier.

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Disadvantages being:

(a) It is extremely less robust due to the fact that random changes of the LSBs destroy the coded

watermark.

(b) It is quite unlikely that the watermark would survive the analog to digital conversion and

vice versa.

2. Quantization Method

This scheme divides an audio signal into samples and then quantizes a value for each sample.

Then the quantized value of each sample is modified based on the watermark bit to be

embedded. In the scalar quantization method a quantization step is decided on whose basis the

quantized value of the sample is generated by using the quantization function. It is with the use

of quantization step only that the value of the sample is modifiied with regard to the bit being

inserted. The detection process is exactly the reverse of the insertion process.

The main advantages of this method are:

(a) It is very simple to implement

(b) It is a blind algorithm.

The disadvantage is:

(a) It cannot survive the noise attacks if the additive noise is larger than the quantization step.

This method can also be characterized as one which uses the information of the audio signal for

embedding the watermark.

3. Addition of Pseudo Random Sequence

In this scheme, the watermark is simply considered to be pseudo random sequence.This

technique takes into account the characteristics of the psycho acoustic model such that added

sequence does not cause any audible effect on the audio signal.

Before embedding the watermark, it is shaped in such a manner that its addition to the signal is

not heard. The shaping of watermark can be done in many ways, one of them is filtering. In this

method, the audio signal is again divided into samples and the shaped pn sequence is added to

each of the samples of the signal or some of the selected samples. The method of addition of the

watermark can be additive, multiplicative etc. In the extraction process, the audio signal is again

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divided into samples and the watermark is extracted from the selected ones or all of them by the

procedure reverse of what was followed for embedding. Now the extracted and the original and

the extracted watermark can be compared to check for the successful detection.

The advantages of this algorithm are:

(a) The watermark can be repeatedly embedded in the audio signal.

(b) It is quite robust against attacks.

The disadvantage being:

(a) The transmission cost of the audio signal goes very high.

4. Echo hiding method

Echo hiding embeds the data into the audio signal by introducing an echo in time

domain. The nature of such echoes is to add resonance to the host audio.

x(n) = s(n) + a:s(n - d)

Here only 1 echo sound is being added but multiple echoes can also be added.

Here in this method the host audio signal is divided into smaller portions. Each portion can be

considered as an independent signal. Now embedding of the watermark into these independent

signals takes place by introducing the bit delays.

As for an instance, binary messages are added by echoing the original signal with 2 delays, either

a d0 sample delay for bit 0 or a d1 sample delay for bit 1. Extraction of the embedded message

involves the detection of the delay. Cepstrum or Autocepstrum analysis are used for these

purposes.

The advantages of Echo hiding method are:

(a) It is quite imperceptible and usually makes the sound rich.

(b) This is a blind algorithm and is highly robust against desynchronization attacks.

The main disadvantages of this method are:

(a) Its increased complexity due to the use of cepstrum analysis for detection.

(b) As the human auditory system is quite sensitive, so echoes ca be very easily detected and

they provide a clue for malicious attack.

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5. Patchwork method

This scheme embeds a special statistic into the audio signal. Two patches are pseudo randomly

selected from the original audio signal. These two patches are nothing but the group of some

samples each. In the simplest patchwork strategy,a constant value d is added to one patch and

subtracted from another. Apart from the additive strategy, multiplicative operations can also be

used for the implementation of the patchwork method in which a single bit of the watermark is

embedded into the signal by multiplying or dividing the sample values of one patch thus,

leaving the other patch intact. The watermark is extracted at the receiver end by the comparison

of energies of the two patches so as to say the expected values of the samples of the two patches

are compared. In case of the addition and subtraction operated patchwork scheme, the difference

of the sample values of the patches is compared with the threshold value to decide whether the

samples contain the watermark or not. The threshold value is decided with the constant value that

is used while embedding the watermark .

Its greatest advantage is:

(a) Since the algorithm does not use the original audio signal for watermark

extraction, it is a blind algorithm.

(b) This scheme can also be implemented in transform domain [26] as well and

in that case the modifications would be done on the transform coefficients of

the samples in the patches .

Disadvantage of this scheme is:

(a) It is less robust against attacks if position of patches is known.

6. Spread Spectrum method

The spread spectrum technique encrypts information by spreading the encrypted data across a

large frequency spectrum. In this technique the watermark is first shaped and then it is spread

over the entire audio signal by the use of various spread spectrum techniques. The spread

spectrum technique can also be implemented in the transform domain. In Direct Sequence

Spread Spectrum techniques, spreading is accomplished by modulating the original signal with a

sequence of pseudo random binary pulses known as chips. In the embedding process, the audio

data is coded as a binary string. The code is modulated by a carrier wave and multiplied by the

pseudo-random noise sequence, having a wide frequency spectrum. It spreads the frequency

26

spectrum [29] of the data over the available frequency band. This spread data sequence is

attenuated and added to the original file. For extraction the watermarked signal is again

multiplied by the same pseudo-random noise sequence. The watermark is spread over so many

components of the signal

so that the energy of any component is very small and certainly undetectable.

The advantages of this technique are:

(a) It is a simple to implement.

(b) It is a blind algorithm.

Its greatest disadvantage is:

(a) This method is highly fragile against de-synchronization attacks.

3.3 Frequency Domain Techniques

Audio signals are transformed from time domain to frequency domain to enable effective

embedding of the watermark. Transform domain techniques allow the embedding of the

watermark in the perceptually significant components of the audio signal. The transform

domain techniques are more robust against attacks as compared to the time domain techniques

but the drawback being the high computation requirement. Various time domain techniques can

be incorporated with the transform domain techniques to make more robust methods of audio

watermarking.

1. DCT based Watermarking

Watermark message is embedded into the host audio by modifying the DCT coefficients, which

can be regarded as addition of noise to the original audio signal. Audio signals is divided into

frames and DCT is applied to them individually. Shaped watermark signal is then added to the

DC or AC coe_cients of the transformed audio signal. Then inverse DCT is applied to the

frames. The DCT transform divides the signal into three frequency regions namely , low mid and

high. The watermark is fragile when embedded in the low or high frequency region so for

robustness, it is embedded in the mid frequency range. The other reason for not embedding the

watermark in the low frequency region is that it causes audible changes to the signal thereby,

destroying its fidelity. In case of embedding the watermark in high frequency region, the

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problem is of robustness only. The chances of the removal of the watermark are very high by

simple signal processing operations.

For extracting the watermark, DCT needs to be applied to the signal and then from the selected

frames the watermark is extracted by following the procedure reverse to that used for

embedding.

2. DFT based Watermarking

The methodology to embed the watermark in the audio signal is same as DCT. The audio signal

is divided into frames and DFT is applied on them individually. Some or all of the frames can be

used for embedding the watermark. In case the watermark is to be embedded in some frames

then one way for the selection of these frames is on the basis of a secret key. This key is used at

the time of extraction also for taking out the selected frames. The application of DFT divides

the signal into two parts of phase and magnitude. The watermark is embedded into any of these

parts of the DFT coeffcients depending upon the requirement of the application. Prominently the

embedding is done in magnitude part only. Perform the inverse DFT on the frames to reconstruct

the audio signal. For extraction again the same DFT is applied to the signal and from the selected

frames watermark is extracted.

The advantages of this technique are:

(a) It is highly robust against various signal processing attacks.

(b) It is a blind algorithm.

(c) This scheme is more robust to attacks than DCT based watermarking scheme.

The disadvantage is:

(a) The complexity of the procedure involved for watermarking and extraction

is quite high.

3. DWT based Watermarking

DWT based watermarking schemes are on the same pattern as DCT based schemes. The audio

signal is transformed by wavelet transforms using wavelet filters. The common filters for

watermarking are Daubechies Orthogonal Filters, Haar Wavelet Filter and Daubechies Bi-

Orthogonal Filters. The signal is decomposed into several frequencies by these filters. On single

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level decomposition, the signal is decomposed into two parts, high frequencies and low

frequencies. The part containing low frequencies is again decomposed into two parts, high

frequencies and low frequencies. The number of levels in which the signal can be decom-

posed depends upon application and length of signal. The decomposed data thus obtained gives

DWT coefficients. The original signal can again be reconstructed by applying the inverse DWT

scheme.

3.4 Methods used to test Watermark Robustness

The most common method of watermarking audio is to mark every xth

bit in an audio file

depending on the random generator seed calculated from the watermarking key applied to the

audio. These are some of the ways watermarks can be removed from audio files MPEG1 Layer

III (MP3) audio compression

A digital audio compression algorithm that achieves a compression factor of about twelve while

preserving sound quality. What this lossy compression does is remove the frequencies not heard

by the human ear from the audio. If a raw audio file is converted to MP3 at a bit-rate of 128kbps

than roughly 90% of the frequencies are removed. This means that a search for the watermark

needs to find an unaltered length of samples that contains at least 2 watermarked bits to prove the

watermarks existence.

Audio Restoration programs

Audio restoration programs are designed to remove hisses, crackles and pops from audio

recordings. They do this by searching through the wavelength, removing samples that don’t “fit

in” amongst neighbouring samples, and replacing them with an average of the two neighbour

samples. Although the removal of digital watermarks is obviously not a purpose of these

programs, they work remarkably well at doing so as the sample bits inserted to watermark the

audio don’t fit in with their surrounding pixels, and are therefore removed.

Echo Hiding Removal

Echo hiding relies on the fact that we cannot perceive short echoes, eg: 1 millisecond(ms) and

embeds data into a cover audio signal by introducing an echo characterised by its delay and its

relative amplitude compared to surrounding samples. The echo delays are chosen between 0.5

ms and 2 ms and the best relative amplitude of the echo is around 0.8 ms. However specialised

29

software which looks for echoes with a length between 0.5 ms and 2 ms 7(as seen below), can be

used to detect and remove these echoes without effecting sound quality.

Zitter

The simplest and most effective attack on any audio watermarking scheme is to add jitter to the

signal. ”In our first implementation, we split the signal into chunks of 500 samples, either

duplicated or deleted a sample at random in each chunk (resulting in chunks of 499 or 501

samples long) and stuck the chunks back together. This turned out to be almost imperceptible

after altering, even in classical music; but the jitter prevents the marked bits from being located”,

and therefore the watermark is obliterated.

In his paper titled “Audio watermarking: Features, Applications And Algorithms“, Michael

Arnold agrees with the Cambridge team stating that

“one of the greatest challenges [of watermarking] is the robustness against the so-called jitter

attack”.

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CHAPTER 4

ADVANTAGES AND DISADVANTAGES

4.1 Advantages of digital watermarking

The field of digital watermarking is not restricted to digital images. This technique time and

frequency masking properties of human ear to conceal the watermark and make it unaudible.

There are some benefits of this technique as-

1. Uniquely identifies author of copyrighted works.

2. Robust design of digital waetrmark withstand pirating attacks.

3.Embedding watermark is easy.

4. Implementation on PC platform is possible.

There are some military and civilian applications of digital watermarking also.

Military applications

1. Intelligence activities.

2.Traitor tracing.

3. Image tampering detection.

Civilian applications

1. Copyright protection of each digital media in hardcopy or on internet.

2. Intelligent web browsers.

3. Law enforcement for chain of evidence.

Some special watermarking technique uses color separation. So watermarks appears in only one

of the color bands. Therefore watermarks becomes strongly invisible. Whenever the colors are

separated from printing then watermarks becomes visible. This approach is advantageous to

journalists to inspect digital pictures from a photo stockhouse before buying an un-watermarked

versions.

There is an important advantage of invisible fragile watermarks. With such invisible fragile

watermarks, implementation of web based image authentication This web based authentication

includes watermark embedding and authentication system. In case of watermark embedding

system, it is installed in server as application software that any authorized user who access to

server can generate watermark image.The distribution can be done through any network as FTP,

31

e-mail etc. Once image is distributed to externally, client can get authentication web page to get

verification of images. Digital watermarking techniques is having advantages as we seen

earlier.It also have some limits also.

4.2 Disadvantages of digital watermarking

Digital watermarking is recent research field, therefore it’s intrinsic limitations are not

understood yet. The blind watermarking algorithm which is really robust is not in existence

today. Another disadvantage is that owner can erase the watermark. By knowing the exact

content of watermark and algorithms to embeds and retrieve it. It is always possible to make it

unreadable without any significant degradation of the data. Again it is not clear that. if this

drawback will be got around in future, in the meantime ,the possibility of erasing the watermark

or its part ,once it’s content is known must be taken into account when designing a copyright

protection system. As a matter of fact, if anyone is allow to read the watermark, then anyone can

erase it by knowing the embedding algorithm. In some researches, the conclusion comes that not

all watermarking techniques will be useful in resolving ownership disputes. Watermarking does

not prevent image copying as much as it simply makes copied images easier to track down and

detect ownership.

Some watermarks vanish if someone manipulates the image in a program like Photoshop. The

watermarks have been known to weaken or disappear by the time the images were processed for

the Internet. Resizing, compressing and converting images from one file type to another may add

noise to an image or diminish its watermark in such a manner that the watermark becomes

unreadable.

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CHAPTER 5

FUTURE OF DIGITAL WATERMARKINGThe field of digital watermarking is still evolving and is attracting a lot of research interest. The

watermarking problem is inherently more difficult that the problem of encryption, since it is

easier to execute a successful attack on a watermark. In cryptography, a successful attack often

requires deciphering an enciphered message. In the case of digital watermarking, merely

destroying the watermark, usually by slightly distorting the medium containing it, is a successful

attack, even if one cannot decipher or detect any hidden message contained in the medium.The

enormous popularity of the World Wide Web in the early 1990's demonstrated the commercial

potential of offering multimedia resources through the digital networks. Since commercial

interests seek to use the digital networks to offer digital media for profit, they have a strong

interest in protecting their ownership rights.

Digital watermarking has been proposed as one way to protect such interests. Though much

research remains before watermarking systems become robust and widely available, there is

much promise that they will contribute significantly to the protection of proprietary interests of

electronic media. Collateral technology will also be necessary to automate the process of

authentication, non-repudiable transmission and validation. An exhaustive list of watermarking

applications is of course impossible. However, it is interesting to note the increasing interest in

fragile watermarking technologies. Especially applications related to copy protection of bills

with digital watermarks. Various companies have projects in this direction solutions will soon be

available. In addition to technological developments, marketing and business issues are

extremely important and require in-depth analysis and strategic planing. It is very important to

prepare the industry to the usage of digital watermarks and and it is very likely that fully

functioning to convince them of the added value their products can gain if they employ digital

watermarking technologies.

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CHAPTER 6

CONCLUSION

The large need of networked multimedia system has created the need of COPYRIGHT

PROTECTION. It is very important to protect intellectual properties of digital media. Internet

playing an important role of digital data transfer. Digital watermarking is the great solution of the

problem of how to protect copyright. Digital watermarking is the solution for the protection of

legal rights of digital content owner and customer.

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CHAPTER 7

REFERENCE

[1] http://www.wekipedia.org

[2] Kim, H.J., Audio Watermarking Techniques, Paci_c Rim Workshop on Digital

Steganography, Japan, July 2003.

[3] Arnold M., Audio watermarking: Features, Applications and Algorithm, IEEE

International Conference on Multimedia and Expo., vol. 2, pp. 1013-101, 2001.

[4] Cano, R.G., et al, Analysis of Watermarking Schemes, 2nd International

Conference on Electrical and Electronics Engineering (ICEEE) and XI Conference

on Electrical Engineering, Mexico, 2005.

[5] Arnold M, Audio Watermarking, Dr. Dobb's Journal, vol. 26, Issue 11, pp. 21-26,

2001.

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