CAPTCHAs are programs that generate and grade tests to tell humans and computers apart. They distort text, images, or audio that current optical character recognition (OCR) software cannot read but humans can to block bots from accessing websites. While effective, CAPTCHAs must be carefully designed to avoid usability and accessibility issues for different users and ensure they are not easily broken by advances in OCR technology. Continual improvements aim to resolve challenges in current implementations.

1. CAPTCHARavindraShetty 4NM09MCA60

2. TopicsDEFINITION

3. BACKGROUND

4. TYPES

5. APPLICATIONS

6. CONSTRUCTING CAPTCHA

7. BREAKING CAPTCHA

8. ISSUES WITH CAPTCHA

9. CONCLUSIONINTRODUCTIONCAPTCHA – Completely Automated Public Turing test to tell Computers & Humans Apart.

10. Invented by Luis von Ahn,Manuel Blum.

11. It is a program that is a challenge response to test to separate humans from computer programs.Contd…..Generic CAPTCHAs distort letters and numbers:

12. Distorted characters are presented to the user.

13. User has to recognize the distorted letters.

14. If the guessed letters are correct, the user is inferred to be a human & allowed access.Contd…..Humans can read the distorted & noisy text.

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

16. Simple CAPTCHA image:BACKGROUNDWhy CAPTCHA was needed ?

17. Sabotage of Online Polls.

18. Spam e-mails.

19. Abusing free Online accounts.

20. Tampering with rankings on recommendation systems (like EBay, Amazon).What is TURING TEST ?Proposed by Alan Turing.

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.

24. After listening to the answer, if the judge fails to recognize which one is the machine, then the machine passes the test. Contd…CAPTCHA employs a Reverse Turing Test.

25. Judge = CAPTCHA program, participant = user

26. If the user passes CAPTCHA, he is human otherwise it is a machine.Types of CAptchaText Based

27. GIMPY

28. EZ-GIMPY