The document provides an overview of CAPTCHAs, which are programs designed to differentiate humans from bots by presenting tests that humans can pass but computers cannot. It outlines the history of CAPTCHAs, their various applications, and different types of CAPTCHAs, including text-based, graphics-based, and audio-based. Additionally, it discusses challenges in breaking CAPTCHAs and references key literature on the topic.

1. CAPTCHATelling Humans and Computers Apart AutomaticallyPresented by: Preetam Kajal Rout

2. DefinitionHistoryApplication of CAPTCHATypes of CAPTCHABreaking CAPTCHAReferenceAgenda

3. CAPTCHA (Completely Automated Public Turing Test To Tell Computers and Humans Apart).The P for Public means that the code and the data used by a CAPTCHA should be publicly available.T for “Turing Test to Tell” is because CAPTCHAs are like Turing Tests.What is CAPTCHA??

4. CAPTCHA is a program that protects websites against bots by generating and grading tests that humans can pass but current computer programs cannot. For example, humans can read distorted text as the one shown below, but current computer programs can't.What is CAPTCHA??Continues…

5. CAPTCHA was first used by “AltaVista” in 1997.Reduced Spam by 95% for a small period of time.Yahoo! Chat room problem.In September 2000, UdiManber of Yahoo! described this "chat room problem" to researchers at CMU:'bots' were joining on-line chat rooms and irritating the people there by pointing them to advertising sites. How could all 'bots' be refused entry to chat rooms?CMU’s CAPTCHA research.The term CAPTCHA coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas Hopper and John Langford of Carnegie Mellon University. History Behind CAPTCHA

6. Preventing Comment Spam in Blogs.Protecting website registration.Protecting email addresses from scrapers.Online Polls.Preventing dictionary attacks. Application of CAPTCHA

7. Text Based CAPTCHAGimpy

8. ReCAPTCHA

9. Gimpy-r, Google CAPTCHAGraphics Based CAPTCHABongoAudio Based CAPTCHATypes of CAPTCHA

10. Text Based CAPTCHAGIMPYGimpy works by selecting seven words out of a dictionary.

11. Then renders a distorted image containing the words.

12. Then presents a test to its user, which consists of the distorted image and the directions: “type three words appearing in the image.”Type three words appearing in the image.

13. Some Screenshots ofText Based CAPTCHAPictures of CAPTCHA implemented by some popular websites.

14. Graphics Based CAPTCHABongoBONGO asks the user to solve a visual pattern recognition problem.

15. It displays two series of blocks, the left and the right. The blocks in the left series differ from those in the right, and the user must find the characteristic that sets them apart.

16. After seeing the two series of blocks, the user is presented with a single block and is asked to determine whether this block belongs to the left series or to the right.To which side does the block on the bottom belong?