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 In this way, reCAPTCHA’s unique technology improves the process that converts scanned images into plain text, known as Optical Character Recognition (OCR). This technology also powers large scale text scanning projects like Google Books and Google News Archive Search. Having the text version of documents is important because plain text can be searched, easily rendered on mobile devices and displayed to visually impaired users. So we'll be applying the technology within Google not only to increase fraud and spam protection for Google products but also to improve our books and newspaper scanning process.

That's why we're excited to welcome the reCAPTCHA team to Google, and we're committed to delivering the same high level of performance that websites using reCAPTCHA have come to expect. Improving the availability and accessibility of all the information on the Internet is really important to us, so we're looking forward to advancing this technology with the reCAPTCHA team.
http://googleblog.blogspot.com/2009/09/teaching-computers-to-read-google.htmlgoogleblog.blogspot.com/2009/09/teaching-computers-to-read-google.html