CAPTCHA stands for "Completely Automated Public Turing test to tell Computers and Humans Apart". It is an automated test used to distinguish humans from bots online. CAPTCHAs work by displaying distorted text images that are easy for humans to read but difficult for computer programs to decipher. They are useful for preventing bots from abusing internet services like spamming forums or faking online polls. While effective, CAPTCHAs are not perfect and new circumvention methods are constantly being developed, so they require ongoing improvement and alternative approaches.

1. CAPTCHA Presented By : Ashish Madhok MCA-2 SEM 13097019

2. Topics To be Covered : 1). What is a CAPTCHA ? 2). Why it is useful? 3). About CAPTCHA 4). Origin 5). Applications 6). Characteristics 7). Accessibility

3. 8). Circumvention 9). Help against spam 10). Need of a CAPTCHA 11). CAPTCHA-Pros and Cons 12). Guidelines

4. WHAT IS A CAPTCHA ? C ompletely A utomated P ublic T uring test to tell C omputers and H umans A part An automated test that can distinguish between machines and humans online. A type of challenge-response test. Involves one computer (a server).

5. Simple Verification made up of:- The CAPTCHA image and the CAPTCHA code that generates it. A form field into which the code one sees in the CAPTCHA image must be inserted – and an enter button. A separate code which checks that the code inserted manually into the field was correct.

6. WHY IS IT USEFUL ? Designed to prevent BOTS from abusing internet services…BOTS Defend e-commerce systems from bots. Eg-Yahoo. Requirement of a common type of CAPTCHA. Described as Reverse Turing Test.

7. ABOUT CAPTCHA ! Pessimal Print Create a distorted background. High levels of warping on the text. Baffle Text Focuses on making segmentation difficult by adding an angled line.

8. ORIGIN Controlled access to web services in a 1996 manuscript of Moni Naor. A simple CAPTCHA-developed in 1995 by Anton Lam. Other primitive CAPTCHA-developed in 1997 at Alta Vista by Andrei Broder. Developed in 2000 by Vin Ahn and Blum

9. APPLICATIONS 1). Preventing Comment Spam in Blogs. 2). Protecting Website Registration. 3). Online Polls. 4). Preventing Dictionary Attacks. 5). Search Engine Bots. 6). Worms and Spam.

10. CHARACTERISTICS Current computers are unable to accurately solve. Most humans can solve. Does not rely on attacker never having seen the CAPTCHA before. Is able to automatically generate new challenges that require artificial intelligence techniques to solve.

11. CIRCUMVENTION Few approaches to defeat CAPTCHA :- HUMAN SOLVERS INSECURE IMPLEMANTATION COMPUTER CHARACTER RECOGNITION

12. HOW CAN CAPTCHA HELP AGAINST SPAM? Great help in downsizing or diminishing FORM SPAMMING Bots go around the web Find forms Send thousands of e-mails through that Fill in the form – sign up for 100 free email accounts, services or products.

13. IMAGE-RECOGNITION CAPTCHAs Alternative for text based CAPTCHAs POTENTIAL PROBLEMS :- Difficult for a small site to acquire a large dictionary of images. Ask the user to make a binary choice.

14. PROS AND CONS PROS Help to fight automatic bots from spamming web site forms. CONS Not a 100 % spammer proof system Not safe for bank account details or credit card pins Sometimes humans can’t recognize it.

15. GUIDELINES Accessibility Image Security Script Security

16. THANK YOU !!!