A CAPTCHA is a program that protects websites against bots (applications that run automated tasks over the Internet) by generating and grading tests that humans can pass but current computer programs cannot. For example, humans can read distorted text but current computer programs can’t.
CAPTCHA is an acronym for Completely Automated Public Turing test to tell Computers and Humans Apart). A Turing test, named for British mathematician Alan Turing, is a test of a machine’s ability to demonstrate intelligence. A Captcha is sometimes described as a reverse Turing test, because it is administered by a machine and targeted to a human and not vice versa.
The Daily Omnivore 
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