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.

This site is dedicated to easy in implementation, but effective CAPTCHA-solutions.

• KCAPTCHA: free open source PHP-based CAPTCHA (Latest version 2.0, 2011 Jun 07, protection increased).
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• Vulnerable CAPTCHA's examples
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