ReCaptcha kills two birds with two words: This is brilliant. Reminds me of the guys who used porn to lure people into solving captchas for them.
ReCaptcha ensures Web site users are human by requiring them to type in distorted and obfuscated words. The computer knows what one of the words is; the other is an unknown word from a book that’s being digitized. When three people type in the same result for the unknown word, ReCaptcha concludes the human digitization is accurate.