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ANDHRA LOYOLA INSTITUTE OF

ENGINEERING & TECHNOLOGY  ELECTRONICS & COMMUNICATION ENGG

PRESENTATION BY:

Y MURALI

13HP1A0449

  CAPTCHATECHNOLOGY 

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CONTENT

Introduction

Definition

 Bascilly what a ‘Captcha do ?

How does Captcha work?

Types of Captchas

Breaking Captchas

 ApplicationsConclusion

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INTRODUCTION

Computers and Humans are apart , atechnique used by a computer to tell if it isinteracting with human or some other

computer. It is needed because activities such asonline commerce transactions, search

engine submissions, Web polls, Webregistrations, free e-mail serviceregistration and other automated services.

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 BASICALLY WHAT A ‘CAPTCHA

DO’ ?

In order to validate the digital transaction, using

the CAPTCHA system the user is presented with adistorted word typically placed on top of a distortedbackground. The user must type the word into a field in

order to complete the process.

 Computers have a difficult time decoding the distortedwords while humans can easily decipher the text.

 Some CAPTCHAs now use pictures instead of words wherethe user is presented with a series of pictures and askedwhat the common element among all of the pictures is.

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HOW DOES A CAPTCHA WORKS?

  A CAPTCHA image shows a random string whichthe user has to type to submit a form.

This is a simple problem for humans, but a veryhard problem for computers which have to use

character recognition, especially, because thedisplayed string is alienated in a way, which makesit very hard for a computer to decode. 

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TYPES OF CAPTCHA

 Text based• Gimpy, ez-gimpy

• Gimpy-r, Google CAPTCHA

•

Simard’s HIP (MSN)  Graphic based

• Bongo

• Pix

  Audio based

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TEXT BASED CAPTCHAS

 Gimpy, ez-gimpy• Pick a word or words from a small dictionary

• Distort them and add noise and background

 Gimpy-r, Google’s CAPTCHA• Pick random letters

• Distort them, add noise and background

 Simard’s HIP• Pick random letters and numbers

• Distort them and add arcs

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GRAPHIC BASED CAPTCHAS

 Bongo• Display two series of blocks

• User must find the characteristic

that sets the two series apart

• User is asked to determine whichseries each of four single blocks

belongs to

• Difference? thick vs. thin lines

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GRAPHIC BASED CAPTCHAS

 PIX• Create a large database of labeled

images

• Pick a concrete object

• Pick four images of the object from theimages database

• Distort the images

• Ask the user to pick the object for a list

of words

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BREAKING CAPTCHAS

Most text based CAPTCHAs have been broken by

software• OCR

• Segmentation

Other CAPTCHAs were broken by streaming the tests

for unsuspecting users to solve.

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 APPLICATIONS

Online polls

Search engine bots

spams

Search Engine Bots

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CONCLUSION

CAPTCHAS are any software that distinguishes

human and machine.

Research in CAPTCHAS implies advancement inmaking computers understand how human

thinks.

Internet companies are making billions of dollarsevery year, their security and services quality

matters and so does the advancement in

CAPTCHA technology.

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THANK YOU!

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