Presented By

Vibhute J.B.

Class : M.Sc. (CS)

IntroductionHistoryTypes of CaptchaProcess of CaptchaBreaking CaptchaRe-CaptchaBenefitsReference

IntroductionCompletely Automated Public Turing tests to

tell Computers and Humans Apart.

Captcha is a challenge response test used in computing to ensure that the response is not generated by computer.

Captcha requires that the user types letters or digits from distorted image appears on screen.

History First developed by Alta Vista in 1997.

The term coined in 2000 by Luis von Ahn, Manuel Blum and Nicholas j.

Hopper of Carnegie Mellon university and john

Langford of IBM.

Types of CAPTCHAsText based

Gimpy, ez-gimpy

Gimpy-r, Google CAPTCHA

Simard’s HIP (MSN)

Graphic based

Bongo

Pix

Audio based

Text Based CAPTCHAsGimpy, 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

Text Based CAPTCHAs Gimpy , Ez-Gimpy

Gimpy-r, Google’s CAPTCHA

Simcard’s HIP (MSN)

Graphic Based CAPTCHAsBongo:

Display two series of blocks

User must find the characteristic that sets the two series apart

User is asked to determine which series each of four single blocks belongs to

Difference? thick vs. thin lines

Graphic Based CAPTCHAsPIX:

Create a large database of labeled images

Pick a concrete object

Pick four images of the object from the images database

Distort the images

Ask the user to pick the object for a list of words

Audio Based CAPTCHAsPick a word or a sequence of numbers at

random

Render them into an audio clip using a TTS software

Distort the audio clip

Ask the user to identify and type the word or numbers

The ProcessGenerate CAPTCHA

Align CAPTCHA

Cut Captcha

Transform CAPTCHA

Decode CAPTCHA

Generate CAPTCHA

CAPTCHA generated with our Mathematical code.

Align CAPTCHA

Remove gridlines.

Undo angle of rotation

Cut CAPTCHA

Cut CAPTCHA cut into 5 pieces.

Transform CAPTCHA Perform the HWT on each of the 5 pieces.

Breaking CAPTCHAs 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.

Re-Captcha

Free captcha service that helps to digitize books, newspaper and old time radio shows.

Recaptcha improves the process of digitizing books by sending words that can’t be read by computers to the web in form of captchas for human to decipher

Working of Re-Captcha

Two words are shown, one word is known as control word and another one is known as a questionable word

System assumes that if human types the control word correctly, then the questionable word is also correct

Re-Captcha Image

Benefits

The database already exists and is public.

The database is constantly being updated and maintained.

Adding “concrete object” to the dictionary is virtually instantaneous.

Distortion prevents caching hacks.

Quick expiration limits streaming hacks.

Reference http://www.captcha.net/

http://www.blogtoplist.com/rss/captcha.html

http://www.gnu.org/licenses/gpl.html

http://www.white-hat-web-design.co.uk/articles/php-captcha.php

Thank You……..