You have almost certainly come across a CAPTCHA before if you’ve tried to sign up for a webmail account or a forum.
A CAPTCHA is a type of challenge-response test used in computing to ensure that the response is not generated by a computer. The process usually involves one computer (a server) asking a user to complete a simple test which the computer is able to generate and grade. Because other computers are unable to solve the CAPTCHA, any user entering a correct solution is presumed to be human.
This has developed into a kind of arms race with spammers come up with better CAPTCHA solving software and organisations trying to improve their CAPTCHA generating algorithms.
Throwing themselves into the ring is reCAPTCHA with a brilliant new twist on the idea because reCAPTCHA has two words. Why? reCAPTCHA is more than a CAPTCHA, it also helps to digitize old books. One of the words in reCAPTCHA is a word that the computer knows what it is, much like a normal CAPTCHA. However, the other word is a word that the computer can’t read. When you solve a reCAPTCHA, we not only check that you are a human, but use the result on the other word to help read the book!
