title: reCAPTCHA: human-based character recognition via Web security measures.
abstract: CAPTCHAs (Completely Automated Public Turing test to tell Computers and Humans Apart) are widespread security measures on the World Wide Web that prevent automated programs from abusing online services. They do so by asking humans to perform a task that computers cannot yet perform, such as deciphering distorted characters. Our research explored whether such human effort can be channeled into a useful purpose: helping to digitize old printed material by asking users to decipher scanned words from books that computerized optical character recognition failed to recognize. We showed that this method can transcribe text with a word accuracy exceeding 99%, matching the guarantee of professional human transcribers. Our apparatus is deployed in more than 40,000 Web sites and has transcribed over 440 million words.
authors.affiliation: Computer Science Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA. biglou@cs.cmu.edu
authors.forename: Luis
authors.initials: L
authors.lastname: von Ahn
authors.forename: Benjamin
authors.initials: B
authors.lastname: Maurer
authors.forename: Colin
authors.initials: C
authors.lastname: McMillen
authors.forename: David
authors.initials: D
authors.lastname: Abraham
authors.forename: Manuel
authors.initials: M
authors.lastname: Blum