Why captcha

you might be in thinking the a code is needed to be entered when we are signing up a new mail or in context where conformation is needed. The twisted letters some thing similar to below image are called CAPTCHA.


what is a CAPTCHA?
  A captch is a program that which protects web sites form bots by generating and grading tests that only human can pass but not the current computer program. These can be read only by human being not by the robots.

          The term CAPTCHA (for Completely Automated Public Turing Test To Tell Computer and Humans Apart) was came in to picture in 2000 by Luis von Ahn, Manuel Blum, Nicholas Hopper and John Langford of Carnegie Mellon University.

credits to captcha.net

Captcha has several application for practical security: 

1. preventing commenting spam in blogs
2. protecting web sites registration
3. Protecting Email Addresses From Scrapers
4. Online Polls
5. Preventing Dictionary Attacks
6. Search Engine Bots
7. Worms and Spam

Why captcha