1. Presented By Vibhute J.B. Class : M.Sc. (CS)
CAPTCHA
Presented By
Vibhute J.B.
Class : M.Sc. (CS)

2. Introduction History Types of Captcha Process of Captcha Breaking Captcha Re-Captcha Benefits Reference

3. Introduction
Completely 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.

4. 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.

5. Types of CAPTCHAs Text based Gimpy, ez-gimpy Gimpy-r, Google CAPTCHA
Simard’s HIP (MSN)
Graphic based
Bongo
Pix
Audio based

6. 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

7. Text Based CAPTCHAs Gimpy-r, Google’s CAPTCHA Simcard’s HIP (MSN)
Gimpy , Ez-Gimpy
Gimpy-r, Google’s CAPTCHA
Simcard’s HIP (MSN)

8. 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 which series each of four single blocks belongs to
Difference? thick vs. thin lines

9. Graphic Based CAPTCHAs
PIX:
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

10. Audio Based CAPTCHAs Pick 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

11. The Process Generate CAPTCHA Align CAPTCHA Cut Captcha
Transform CAPTCHA
Decode CAPTCHA

12. Generate CAPTCHA
CAPTCHA generated with our
Mathematical code.

13. Align CAPTCHA
Remove gridlines.
Undo angle of rotation

14. Cut CAPTCHA
Cut CAPTCHA cut into 5 pieces.

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

16. 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.

17. 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

18. 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

19. Re-Captcha Image

20. 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.

21. Reference http://www.captcha.net/

22. Thank You……..