ReCaptcha

http://recaptcha.net/learnmore.html

reCAPTCHA improves the process of digitizing books by sending words that cannot be read by computers to the Web in the form of CAPTCHAs for humans to decipher. More specifically, each word that cannot be read correctly by OCR is placed on an image and used as a CAPTCHA. This is possible because most OCR programs alert you when a word cannot be read correctly.

It’s rare that I see a really admirable use of computer cycles. This solves a social problem while providing a needed service.

[tags]recaptcha, nifty use of cycles[/tags]