Published at LXer:
Many Web forms these days feature a Completely Automated Public Turing test to tell Computers and Humans Apart (CAPTCHA) as an effort to stop people from setting up computers to automatically fill in Web forms. A typical CAPTCHA is an image with some numbers and letters in it with distortion and/or background noise, and a Web form input field where you are to enter the numbers and letters from the image. This article investigates three CAPTCHA applications that you can use on a PHP Web site.
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