1. CAPTCHA RavindraShetty 4NM09MCA60

3. BACKGROUND

4. TYPES

5. APPLICATIONS

6. CONSTRUCTING CAPTCHA

7. BREAKING CAPTCHA

8. ISSUES WITH CAPTCHA

10. Invented by Luis von Ahn,Manuel Blum.

12. Distorted characters are presented to the user.

13. User has to recognize the distorted letters.

15. Current OCRs(Optical Character Recognition) cannot read them.

17. Sabotage of Online Polls.

18. Spam e-mails.

19. Abusing free Online accounts.

21. To test a machine’s level of intelligence.

22. Human judge asks questions to two participants, one is a machine & the other human.

23. The judge doesn’t know which is which.

25. Judge = CAPTCHA program, participant = user

27. GIMPY

28. EZ-GIMPY

29. MSNS Passport Service CAPTCHAs

30. Graphics Based CAPTCHAs

32. What is the sum of three & thirty-five ?

33. If today is Saturday, what is day after tomorrow ?

34. Which of mango, table & water is a fruit ?

35. Very effective, needs a large question bank.

37. Picks up 10 random words from dictionary & distorts, fills with noise.

38. User has to recognize at least 3 words.

40. Yahoo used this version in Messenger.

41. Has only 1 random string of characters.

42. Not a dictionary word, so not prone to dictionary attack.

44. Use of 8 characters.

45. Warping is used to distort.

46. Very strong implementation, hasn’t been broken.

49. User has to solve a pattern recognition problem.

50. Has to tell the distinct characteristic between two sets of figures.

52. It shows a set of images, user has to recognize the common feature among those.

54. User listens & enters the spoken word.

55. Helps visually disabled users.

57. Prevent web registration abuse, protect passwords from brute-force attack.

58. Prevent comment spam & spam e-mails.

60. Used in Google books project.

61. Two words are shown, the program knows the first word.

62. If the user enter the first word correctly, it assumes that the second unknown word will also be entered correctly.

64. Don’t store CAPTCHA solution in web page’s metadata.

65. A CAPTCHA is no good if it doesn’t distort.

66. Need a large database of different CAPTCHA questions.

68. Persist the correct answer.

69. Present the question to the user.

70. Evaluate the answer, if incorrect start again- Generate a different CAPTCHA.

72. Convert CAPTCHA into Grey scale.

73. Detect patterns in the image corresponding to the characters

74. Greg Mori & JitendraMalik have broken text CAPTCHAs Ex:- Easy Gimpy

76. Segmentation

77. Locate possible letters in the image.

78. Construct graph of consisting letters.

79. Find out the possible words from the graph, use scores to rank

80. Roll = 11.94

82. Spammer encounters a CAPTCHA

83. That CAPTCHA is copied to another site

84. Humans are baited, Ex:- free MP3s, free wallpapers, etc.

85. To get those MP3s or wallpapers, users are told to solve the copied CAPTCHA.

86. Then the solution is routed back to the spammer.Solution – Fix a time-to-live period for a question.

88. W3C mandates web to be accessible to all people.

89. Some CAPTCHAs are in accessible to visually impaired, cognitively challenged people.

90. Compatibility issue

91. Java script may be needed to be activated in browsers.

93. They help advance AI knowledge.

95. THANK YOU