Info Tech Guide

A Captcha is program used to verify that a human, rather than a computer, is entering data. Captchas are commonly seen at the end of online forms and ask the user to enter text from a distorted image. The text in the image may be wavy, have lines through it, or may be highly irregular, making it nearly impossible for an automated program to recognize it. Some captchas are so distorted that they can be difficult for humans to recognize as well. Fortunately, most captchas allow the user to regenerate the image if the text is too difficult to read. Some even include an auditory pronunciation feature.

By requiring a captcha response, webmasters can prevent automated programs, or "bots," from filling out forms online. This prevents spam from being sent through website forms and ensures that wikis, such as Wikipedia, are only edited by humans. Captchas are also used by websites to make sure users don't bog down the server with repeated requests. While captchas may be a minor inconvenience to the user, they can save webmasters a lot of hassle by fending off automated programs.

A Captcha is a challenge-response system test designed to differentiate humans from automated programs. A CAPTCHA differentiates between human and bot by setting some task that is easy for most humans to perform but is more difficult and time-consuming for current bots to complete.

CAPTCHAs are often used to stop bots and other automated programs from using blogs to affect search engine rankings, signing up for e-mail accounts to send out spam or take part in on-line polls.

Frequently, a CAPTCHA features an image file of slightly distorted alphanumeric characters. A human can usually read the characters in the image without too much difficulty. A bot program is able to recognize that the content contains an image , but it has no idea what the image is. To accomodate the visually-impaired, some CAPTCHAs use audio files. In such a system, the human listens to a series of letters or short words and types what he hears to prove he is not a bot.

The term CAPTCHA was coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas J. Hopper, and John Langford. It is a contrived acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart." Carnegie Mellon University attempted to trademark the term,but the trademark application was abandoned on 21 April 2008