Since the 1980s–1990s, users have wanted to make text illegible to computers. A normal CAPTCHA test only appears if the user acts like a bot, such as when they request webpages, or click links too fast. Newer CAPTCHAs look at the user's behaviour on the internet, to prove that they are a human. CAPTCHAs are designed so that humans can complete them, while most robots cannot. Many websites use CAPTCHA effectively to prevent bot raiding.

PurposeĬAPTCHAs' purpose is to prevent spam on websites, such as promotion spam, registration spam, and data scraping, and bots are less likely to abuse websites with spamming if those websites use CAPTCHA. It takes the average person approximately 10 seconds to solve a typical CAPTCHA. Two widely used CAPTCHA services are hCaptcha, an independent company, and reCAPTCHA, offered by Google. 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. This form of CAPTCHA requires entering a sequence of letters or numbers in a distorted image. It is a contrived acronym for 'Completely Automated Public Turing test to tell Computers and Humans Apart.' A historically common type of CAPTCHA (displayed as Version 1.0 ) was first invented in 1997 by two groups working in parallel.

The term was coined in 2003 by Luis von Ahn, Manuel Blum, Nicholas J. tʃ ə/ 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. This CAPTCHA (Version 1 ) of 'smwm' obscures its message from computer interpretation by twisting the letters and adding a slight background color gradient.Ī CAPTCHA ( / ˈ k æ p. This article may need to be rewritten to comply with Wikipedia's quality standards, as it feels like an essay criticising CAPTCHA.

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