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From Digital Watermarking to Multimedia Forensics:
How can they help to detect lost identities in multimedia work?
Shujun LI (李树钧 )Senior Lecturer
Department of ComputingUniversity of Surrey
http://www.hooklee.com
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Outline
- Where is University of Surrey?
- “Current” “Solution”: Identities as Metadata- “New” Solutions?
- Active Solution: Digital Watermarking- Passive Solution: Multimedia Forensics- Active Solution: Registering Your Work?
- Expertise of Researchers at Surrey Computing
- Questions and Answers
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Central London Guildford, Surrey
Highway A3: 33 milesFastest train: 33 mins
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Guildford Station Surrey Computing
Guildford Railway Station Surrey Computing (by walk):17 mins
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Dept. Computing @ University of Surrey
Detecting Lost Identities:From Digital Watermarking to Multimedia Forensics
Identities in Multimedia Work
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Current Solution: Identities as Metadata
- Many media formats support metadata (e.g. Exif, IPTC IIM and XMP) as part of their file headers.
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Identities as Metadata: Problems
- Location is public Unauthorised removal- Content is public Unauthorised modification
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Solutions?
- Active Solution: Digital Watermarking- Making metadata dependent on the content itself and
secret Change the metadata = Change the content!- Active = Some information (watermark) needs
embedding into the protected work when/after the multimedia work is created in an additional process.
- Passive Solution: Multimedia Forensics- Discovering information which was NOT actively
embedded into the multimedia work.- Where is the information from? – Left by the capturing
device/creator as part of the natural process.- Multimedia work Device Owner (Author?)
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Solutions? (continued)
- Active Solution: Register Your Work?- Register your multimedia work at a trusted center (e.g.
one maintained by the IPO) actively.- It does not need to be done by the author, but can be
done by the capturing device (when it connects to the Internet) or some software (when a piece of multimedia work is uploaded to the Web).
- One does not have to register the whole work, but only its (cryptographic and/or perceptual) hash value plus some identification information (e.g. device ID, username).
- This can supplement the other two solutions.
Detecting Lost Identities:From Digital Watermarking to Multimedia Forensics
Active Solution:Digital Watermarking
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What is a digital watermark?
- A digital watermark is a digital artefact embedded into a cover work which is also a digital artefact.
- It can be a textual message, an image or just a random number (like an ID) represented as a number of bits.
- The process of embedding a digital watermark is called digital watermarking.
- It may be visible or invisible. When it is visible, it mimics watermarks printed on the paper.
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Identities as watermark
- A typical application of digital watermarking is copyright protection.- The watermark is a copyright claim: “All rights reserved
Shujun Li, University of Surrey 2012”.- The watermark needs to be secured! – Only the owner
knows the embedding/extraction key.- The key can be disclosed to settle an ownership dispute.
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Conflicting objectives
- Fidelity/Imperceptibility = The watermark should not degrade the perceptual quality to compromise the value of the protected work.
- Security = Surviving malicious attacks- Capacity = More information embedded- Robustness/Fragility = Surviving benign processing
- It is impossible to have an ideal system!
Robustness / Fragility
Fidelity / Imperceptibility
S e c u r i t y
Capacity
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Security is complicated!
- Watermarked-only attack- The attacker has a number of watermarked works only.
- Known-watermark/message attack- The attacker has access to a number of watermarked works and
the watermark(s) embedded in them.- Known-cover/original attack
- The attacker has access to a number of watermarked works and the original cover work(s).
- Chosen-cover/original attack- The attacker can choose the original cover work(s) in which the
watermark(s) is/are embedded.- Known-detector attack
- The attacker has access to the detector.
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Security is complicated!
- Unauthorized watermark embedding- The attacker wants to forge a watermark or modify a watermark
already embedded.- Example: to claim the ownership over a work of others.
- Unauthorized watermark removal- The attacker wants to remove the watermark embedded in a
watermarked work.- Example: to remove the watermark/fingerprint in a watermarked
(copyrighted) work.- Unauthorized watermark detection
- The attacker wants to detect the watermark embedded in a watermarked work.
- Example: to disclose the author of a watermarked work.
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Watermarking by cameras
- Digital cameras capable of embedding digital watermarks do (or did?) exist.- Epson PhotoPC 3000Z/700/750Z/800/800Z- Kodak DC200/DC260/DC290
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Watermarking by cameras
- Paul Blythe and Jessica Fridrich, “Secure Digital Camera,” in Proceedings of 4th Annual Digital Forensic Research Workshop (DFRWS 2004), Baltimore, August 11-13, 2004- Watermark = Biometric (iris) patterns of the
photographer + Cryptographic hash of the image + Time, Date + …
- The watermarking process is LOSSLESS. The distortion caused by the watermark can be restored without any error.
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Digital watermarking: problems
- Impossible to have an ideal watermarking scheme.- If the accuracy is not too high, can the results be still used?- Can some (advanced) attacks be ignored?
- Configuring a watermarking scheme is very complicated.- How to balance different objectives?
- Require actions from both vendors and users.- Vendors provide the feature.- Users learn and use it properly.
- Somebody needs to keep the secret key and disclose it when needed.
- …
Detecting Lost Identities:From Digital Watermarking to Multimedia Forensics
Passive Solution:Multimedia Forensics
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What is multimedia forensics?
- A new research topic developed since late 1990s.- Multimedia forensics = Forensic analysis of
multimedia data and devices.- Source identification = What produced this work?
Was this work computer generated or captured by a device? Who produced this work?
- Forgery detection = Is this work genuine? Which part of this work is genuine?
- Processing history recovery = What has happened on this work? What is the parameter of a step of the processing history?
- …
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Better than digital watermarking?
- Yes- No need to design an (ideal) algorithm.- No need to configure an algorithm.- No action required for vendors or users.
- No- Only limited information can be extracted.- Accuracy of extracted information could be even lower.- Often require training = No a prior information about
something, nothing can be extracted about it.- Anti-forensics can defeat forensics!
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Identifying authors
- Forensic (behavioural) biometrics- Like handwritten signatures, intrinsic
features in multimedia work may be linked to its authors’ identities.
- BBC News, New Vincent van Gogh painting identified, 9 November 2013- “The museum said the painting was
authenticated by letters, style and the physical materials used.”
- All could be identified via some multimedia forensic techniques.
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Identifying devices
- Source identification- Identifying the source device producing a digital
audio/image/video file.- How can this be done without a watermark?
- Different hardware and software components in different models
- Different intrinsic features of individual devices (noise patterns, manufacturing deviations, dust spots and dead points on camera sensor array, …)
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Linking devices with authors
- When the device of the author can be obtained.- Sometimes only the model matters.
- When some other pieces of multimedia work produced by the same device have their author(s) identified.- So “Register Your Sample Work” is important?
- When the device’s intrinsic features are registered at a trusted party.- So “Register Your Device” is important?
Detecting Lost Identities:From Digital Watermarking to Multimedia Forensics
Expertise of Researchers @Surrey Computing
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MSF Group @ Surrey Computing
- MSF = Multimedia, Security and Forensics- 6 academics
- Prof Anthony TS Ho (Group Head / HoD)- Prof Jianmin Jiang- Dr Johann A Briffa (Lecturer)- Dr Shujun Li (Senior Lecturer)- Dr Norman Poh (Lecturer)- Dr Stephan Wesemeyer (Tutor)
- 1 postdoctoral fellow- 13 PhD students (including 4 jointly with other
research groups)
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MSF Group @ Surrey Computing
- Multimedia Security- Digital and Multimedia Forensics- Cyber Security and Privacy- Biometrics and Health Informatics- Multimedia Coding & Visual Quality
Assessment- Digital Media Content Analysis- Big Data Analytics
Detecting Lost Identities:From Digital Watermarking to Multimedia Forensics
Thanks for your attention!
Questions + Answers