CAPTCHA is an acronym for "Completely Automatic Public Turing Test to Tell Computers and Humans Apart". It is a task, that human can easily solve, but computer not. It is intended to determine whether or not the user is human. Usually, CAPTCHA requires that the user type the letters and digits of a noised and distorted image. You do not even find analogues such scripts freely available on the Internet. Do not believe it?
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