1. A SEMINAR ON
CAPTCHA
By-
ABHIMANYU SOOD
0902810002 (C.S.E.)
DEPARTMENT OF COMPUTER SCEINCE AND ENGINEERING
IDEAL INSTITUTE OF TECHNOLOGY, GHAZIABAD [U.P.]
(Approved by AICTE and affiliated to GBTU, Lucknow U.P.)
2011-2012

2. CAPTCHA: Outline
 Meaning of CAPTCHA
 Origin of CAPTCHA
 Different types of CAPTCHA
 Application of CAPTCHA
 Properties of CAPTCHA
 Circumvention/Breaking of CAPTCHA
 Reference
 Conclusion

3. CAPTCHA: Acronym
 Completely
 Automated
 Public
 Turing Test to Tell
 Computers and
 Humans
 Apart

4. CAPTCHA: Meaning
 Completely - Whole
 Automated - Made by machine
 Public - Universally known
 Turing Test to Tell - Test presented by Alan Turing
 Computers and
 Humans
 Apart

5. CAPTCHA: Example

6. CAPTCHA: Origin
 1997: Andrei Broder at AltaVista wanted to
prevent bots from automatically submitting
sites for indexing
 He decided to add a test to the submission page
 He performed a reverse scan through Optical
Character Recognition(OCR) scanner
 2000: Luis von Ahn, Manuel Blum & John
Langford at CMU coined term CAPTCHA

7. CAPTCHA: Deciding Human or
Bot?
 A puzzle or problem that is easy for
humans to solve and very difficult for
computers is given
 If the puzzle is solved correctly, you are
considered human and can continue
 Also known as reverse Turing Test-
Human Interaction Proof.

8. CAPTCHA: Basic types
Printed CAPTCHA
Handwritten CAPTCHA

9. PRINTED CAPTCHA
 Printed CAPTCHA is difficult to break
 Lots of algorithms are available to
generate these
 Computers cannot identify these easily
 Two major types are there viz. Baffle
text, Pessimal print.

10. PRINTED CAPTCHA: Baffle
 Developed by Monica Chew and Henry Baird
 Uses pronounceable English characters(with
various masking techniques)that are not present
in English dictionary

11. PRINTED CAPTCHA: Pessimal
 Developed by Allison Coates and Henry Baird
and Richard Fateman
 Uses the degradation model simulating physical
defects caused by printing and scanning of
printed text

12. HANDWRITTEN CAPTCHA
 Less frequently used because computers can
easily identify the handwriting rather than text
images (OCR Scanners)
 Use of transformations by adding lines, arcs,
circles etc.

13. HANDWRITTEN CAPTCHA: Example

14. CAPTCHA: Advanced Types
 Text based
 Ez-gimpy
 R-gimpy (Google)
 Simard’s HIP (MSN)
 Graphic based
 Bongo
 Pix

15. CAPTCHA: Advanced Types
 Audio based
 Face Recognition
 Logic Puzzles
 KittenAuth

16. CAPTCHA: Text Based
 Gimpy, ez-gimpy
 Pick a word or words from a dictionary
 Distort them and, add noise and background
 Gimpy-r, Google’s CAPTCHA
 Pick random letters
 Distort them and, add noise and background

17. CAPTCHA: Text Based(Gimpy)
EZ-GYMPY
R-GIMPY

18. CAPTCHA: Text Based
 Simard’s HIP
 Pick random letters and numbers
 Distort them and add arcs

19. CAPTCHA: Graphics Based
(Bongo)
 A visual recognition problem
 Two sets of shapes with a distinguishing characteristic
 Must choose which set the shape belongs to

20. CAPTCHA: Graphics Based (Pix)
 A database of labeled images of recognizable objects
 Randomly chooses an object and displays N pictures of it
 Must correctly identify the object
 Pictures can or cannot be distorted

21. CAPTCHA: Audio
 Pick a word or a sequence of numbers at
random
 Render them into an audio clip using a Text
To Speech (TTS) software
 Distort the audio clip
 Ask the user to identify and type the word or
numbers

22. CAPTCHA: Face Recognition

23. CAPTCHA: Logic Puzzles
 Easy trivia questions
 Example: Which of the following is a bird?
Elephant, Tiger, Robin
 Simple mathematical expressions: What is the solution?
(2+2)
 It’s very accommodating to create a big enough
database of these simple logic based puzzles

24. CAPTCHA: KittenAuth
 “The Cutest Human Test”
 A 3x3 matrix of cute animals
 Choose the 3 kittens
 Strategy is to use
animals that look
similar to kittens

25. CAPTCHA:- Application
 Online polls
 Free e-mail services
 Search engines
 Prevention to Worms and spam's
 Preventing dictionary attack
 Newsgroups, Blogs, etc…

26. CAPTCHA:- Application (E-Mail)
Hotmail Registration
Yahoo! Registration

27. CAPTCHA: Properties
 CAPTCHA should be automatically generated and
graded for good performance
 Test can be taken quickly and easily by human users
 Test will accept virtually all human users and reject
software agents
 Test has been able to resist attacks for many years,
despite the technological advances and knowledge of
algorithms, but are they full-proof ??

28. CAPTCHA: Circumvention
(Breaking)
 Introducing bugs in the system, so that it
allows the attacker to completely bypass the
CAPTCHA.
 Improving character recognition software.
 Using cheap Human labour to process the
tests(impractical in real world), & as done by
Humans so the purpose of CAPTCHA still
holds.

29. CAPTCHA: Circumvention
(Breaking)
 Pre-Processing: Removal of background clutter
and noise.
 Classification: Identifying the character in each
region.
 Segmentation: Splitting the image into regions
which each contain a single character.

30. CAPTCHA: Conclusion
 They are crucial to preventing bot attacks
 Hopefully, they will become more user-friendly
to people with disabilities (visual/mental)
 CAPTCHA’s are mainly produced from
Asynchronous Java-script And XML (AJAX) &
using a bit of Hypertext Preprocessor (PHP)
technology
 Various algorithms are present

31. CAPTCHA: Reference
 WIKIPEDIA
 GOOGLE
 http://captchas.net
 Numerous sites that provide various
students like us to gather, discuss & help
each other–
http://www.scribd.com/
http://www.slideshare.net/

32. CAPTCHA:

33. CAPTCHA:
Any
Queries.
?