CAPTCHA

While browsing the net (especially webmail services or blogs) you would have come across images with distorted letters presented to you, which you have to type in to be able to proceed. Ever wondered what they are called, and what they are for?

CAPTCHA stands for ‘Completely Automated Public Turing test to tell Computers and Humans Apart’.
A CAPTCHA is a type of challenge-response test used in computing to determine whether the user is human. As computers are unable to solve the CAPTCHA, any user entering a correct solution is presumed to be human.

A CAPTCHA is sometimes described as a reverse Turing test, because it is administered by a machine and targeted to a human, in contrast to the standard Turing test that is administered by a human and targeted to a machine.

CAPTCHAs can be deployed to protect systems vulnerable to e-mail spam, such as the webmail services of Gmail, Hotmail etc. CAPTCHAs have also found active use in stopping automated posting to blogs or forums, which may be for commercial promotion, harassment or vandalism.

So next time you 'solve' and type in the obscure letters presented to you in an image, you know what it is for and you have a name for it. :)

Want a hands-on experience of CAPTCHA right now? Try posting a comment on this blog :)