This strikes me as interesting, because on a NPR show, not too long ago, I heard the inventer of Captcha say that he was working on a system, whereby users could be novelly employed as book translators. The way it worked, is if a computer scan couldn't reproduce the book's page photo as readable text, those text fragments would be forwarded to the Captcha database, and would be sent out to end-users to see how many different eyes might translate it.