ONLINE.

The article discusses Captchas (Completely Automated Public Turing Test to Tell Computers and Humans Apart), which are traditionally used to protect Web sites from malevolent programs. The technique, which requires users to translate garbled text to prove that they are humans, is now being used to help preserve the texts of thousands of important books. Luis von Ahn, the scientist who invented Captchas, is taking book words that are hard to capture through scanning and allowing random Internet users to translate the text.