CAPTCHA is an obvious item in any programmer’s toolkit and a common item on any form presented on a public web page. It is a code that is generated through a program, and is presented to visitor as a distorted image string while being readable by human. Visitor needs to read the characters, and needs to type those in the text-box provided. The program validates the text string entered by visitor with that displayed on CAPTCHA image to arrive at conclusion if the visitor is human or a spam bot.
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