I'm sure by now you have encountered a Captcha - a little form that verifies you are a human and not one of those annoying spam bots. Unfortunately they have become a necessary part of comment and registration forms. Brunello has used CAPTCHAs on several projects in the past to prevent spam and increase security. Theses days Captchas are being used to help translate and digitize books!
An example of a Re-Captcha form
About 60 million CAPTCHAs are solved by humans around the world every day. In each case, roughly ten seconds of human time are being spent. Individually, that's not a lot of time, but in aggregate these little puzzles consume more than 150,000 hours of work each day. What if we could make positive use of this human effort? reCAPTCHA does exactly that by channeling the effort spent solving CAPTCHAs online into "reading" books.
To archive human knowledge and to make information more accessible to the world, multiple projects are currently digitizing physical books that were written before the computer age. The book pages are being photographically scanned, and then transformed into text using "Optical Character Recognition" (OCR). The transformation into text is useful because scanning a book produces images, which are difficult to store on small devices, expensive to download, and cannot be searched. The problem is that OCR is not perfect.
Captchas help correct OCR mistakes
Learn more about how you can help Re-CAPTCHA prevent spam and translate books at their website:http://recaptcha.net.