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A CAPTCHA or Captcha (pronounced /ˈkæptʃə/) is a type of challenge-response test used in computing to ensure that the response is not generated by a computer.

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A CAPTCHA is a challenge-response test most often placed within web forms to determine whether the user is human. The purpose of CAPTCHA is to block form submissions by spambots ...

Telling Humans and Computers Apart Automatically. A CAPTCHA is a program that can generate and grade tests that humans can pass but current computer programs cannot.

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Get a Free CAPTCHA For Your Site. The reCAPTCHA project at Carnegie Mellon University offers a free, secure and easy to install CAPTCHA implementation.

Professional PHP Captcha Script that generates unique captcha images to stop automated submissions, highly customizable, easy to install and configure.

CAPTCHA ( C ompletely A utomated P ublic T uring test to tell C omputers and H umans A part) A category of technologies used to ensure that a human is

captcha.org - listing every captcha you can think of