reCAPTCHA presents two words. One is known, the other is unknown. The idea is that if you type the known word correctly, then you've typed the unknown word corr

reCAPTCHA presents two words. One is known, the other is unknown. The idea is that if you type the known word correctly, then you've typed the unknown word correctly as well. It also shows the same unknown word to many people as a distributed accuracy check.