Definition of captcha
: a test to prevent spamming software from accessing a website by requiring visitors to the site to solve a simple puzzle (typically by reading and transcribing a series of numbers or letters from a distorted image) in order to gain access <The point of the CAPTCHA is that reading those swirly letters is something that computers aren't very good at. If you can read them, you're probably not a piece of software run by a spammer. — Leviticus Grossman>
Variants of captcha
Origin and Etymology of captcha
Completely Automatic Public Turing test to tell Computers and Humans Apart (with deliberate pun on 1capture)
First Known Use: 2001
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