I’ll admit I didn’t have a clue what reCAPTCHAs were about, and turn out its a very neat idea:

CAPTCHAs work—for digitizing old, damaged texts, manuscripts

Over the course of history, humanity has suffered some horrifying damage to our collective cultural legacy in the form of books and other text lost to accident or neglect. The digitalization of text holds out the promise of permanently preserving the written word in an archive that can be distributed widely and kept safe from accidental damage. This presents archivists with a challenge: the works that are most in need of preservation are likely to already be damaged or distorted, making the use of automated scanning and text processing less likely to succeed. Researchers are now reporting on a successful way to identify the words that computers can’t handle: turn them into CAPTCHAs, and get people to do the work.

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