
ReCAPTACHA with Luis von Ahn
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Luis von Ahn invented CAPTCHA - the system that uses a picture of a word to determine whether you are a human or a computer. But when von Ahn realised just how much time was being wasted by filling in CAPTCHAs he wondered whether that man-power could be used for something good. Now the very same process is digitising millions of books, that are available for free, as von Ahn told Chris Smith.