Stumbled into this via a Webware post about Southwest shutting down boarding pass sniping site Pass-a-Matic.
Re-CAPTCHA is a Carnegie Melon University project that repurposes those CAPTCHA verification boxes (last discussed by us here) to help digitize books.
The basic idea is to take words that optical scanners can't recognize, turn them into CAPTCHAs, and then use crowdsourcing ala Mechanical Turk to do the heavy lifting. It's all pretty clever.
More details here.