Prove You're Human and Save a Book

People typically fill out Captchas so Web sites can verify that a human, rather than a spam bot, is behind the request for a new e-mail address, log-in, or membership. But with ReCaptchas, which are double-word tests, humans are also helping machines better recognize faded-ink or blurry words that have been digitally scanned from old newspapers or books--text that's difficult for a computer to recognize optically. That way, people will eventually be able to sift through print archives with a more intelligent search engine.

"We're reusing wasted human cycles," von Ahn, 28, said while speaking at a robotics conference here recently.

The venture involves putting millions of eyes on words printed in roughly 47,000 newspapers, with various counts of pages.

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.