Mind utterly blown. Incredible.

Von Ahn watched the work on CAPTCHA and decided it had potential beyond distinguishing humans from robots — the extra 10 seconds people were taking to access their email and other accounts could be put to use. In 2006, von Ahn launched reCAPTCHA. Unlike its predecessor, reCAPTCHA challenged users with two distorted words to decode, and looks something like this:

The brilliant twist is that this test isn't just verifying your humanity; it's also putting you to work on decoding a word that a computer can't. The first word in a reCAPTCHA is an automated test generated by the system, but the second usually comes from an old book or newspaper article that a computer scanner is trying (and failing) to digitize. If the person answering the reCAPTCHA gets the first word correct (which the computer knows the answer to), then the system assumes the second word has been translated accurately as well.

Thanks to The Loop for the link.