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PHP Ajax Cookbook by R. Rajesh Jeba Anbiah, Roshan Bhattarai, Milan Sedliak

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Decoding CAPTCHA through canvas

CAPTCHA (or Captcha) is an acronym for Completely Automated Public Turing test to tell Computers and Humans Apart, based on the word 'capture'. It was originally coined by Luis von Ahn, Manuel Blum, Nicholas J. Hopper, and John Langford. CAPTCHA is meant to stop machines and robots from accessing webpage functionalities; it is usually placed in a web page's signup form to ensure only human beings are signing up with the site. Often, it is based on the fact that computers find it difficult to recognize text when presented in image form. More research and advanced techniques of OCR (Optical Character Recognition) are weakening the Captcha concept, which in turn forces further research on Captcha. HTML5's canvas

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