CAPTCHA is an acronym for “Completely Automated Public Turing test to tell Computers and Human Apart” .It is like a challenge-response analysis acclimated to ensure that the specific response is not generated by automated computer programs.
This is what Wikipedia says about reCAPTCHA
reCAPTCHA reCAPTCHA is a system originally developed at Carnegie Mellon University that uses CAPTCHA to help digitize the text of books while protecting websites from bots attempting to access restricted areas.
Now , Google acquired reCAPTCHA on 16th September,2009.Surely the Internet giant must have sought something in reCAPTCHA.It will be noteworthy to mention that currently reCAPCHA is digitizing archives of New York Times.
Currently some of the most popular sites like Facebook,Twitter,StumbleUpon,Yahoo! are using reCAPTCHA.Let’s what’s there in Google’s bag for them.