CAPTCHA

Test to determine whether a user is human / From Wikipedia, the free encyclopedia

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A CAPTCHA (/ˈkæp.tʃə/ KAP-chə) is a type of challenge–response test used in computing to determine whether the user is human in order to deter bot attacks and spam.[1]

Captcha.jpg
This CAPTCHA (Version 1[clarification needed]) of "smwm" obscures its message from computer interpretation by twisting the letters and adding a slight background color gradient.

The term was coined in 2003 by Luis von Ahn, Manuel Blum, Nicholas J. Hopper, and John Langford.[2] It is a contrived acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart."[3] A historically common type of CAPTCHA (displayed as Version 1.0[clarification needed]) was first invented in 1997 by two groups working in parallel. This form of CAPTCHA requires entering a sequence of letters or numbers in a distorted image. Because the test is administered by a computer, in contrast to the standard Turing test that is administered by a human, CAPTCHAs are sometimes described as reverse Turing tests.[4]

Two widely used CAPTCHA services are hCaptcha,[5] an independent company,[6] and reCAPTCHA, offered by Google.[7][8] It takes the average person approximately 10 seconds to solve a typical CAPTCHA.[9]

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