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Novelties

    Rogue programs try their best to register at Web sites and then wreak havoc, but a clever puzzle often bars them from entry: a set of distorted, squiggly letters and numbers that people can decipher and type correctly for admission, but that machines still can’t.
    To stay one jump ahead of fraudsters and their
automated programs, researchers are devising more versions of the puzzles, called captchas, to help sites block abuse that includes spam e-mail, illegal postings and skewed online voting.
    Researchers at Google are testing a new captcha that requires people to turn upright randomly rotated images, like that of a parrot perched temporarily upside-down on a leafy branch. The task is a breeze for people [CONNECTOR] hard for machines.
    The new puzzles could be built around a site’s theme - for instance, cartoons at a Disney site, or objects for sale at eBay, said Rich Gossweiler, a senior research scientist at Google who led the team that developed the system. It can be put in place rapidly, he said, and has an almost limitless supply of images. “Our technique expands the vocabulary of captchas” beyond obfuscated characters, he said.
    The program rejects images like those for human faces that computers have already learned to recognize, he said.
    Luis von Ahn, a professor at Carnegie Mellon University and a pioneer in captcha development, has created a free system, called reCaptcha, now used by about 120,000 sites including Ticketmaster, Craigslist, Facebook, Twitter and The New York Times.
    The system has an unusual twist that provides an added benefit to projects that are digitizing books and papers in archives: the source of the wiggly images that people must decipher is not random. The images are drawn from books and other media that are being digitized in mass projects, but that machines haven’t been able to read because, for instance, the page is wrinkled.
    Automatic character recognition lets people who are having the work scanned know which words it cannot read. These are the words that recaptcha farms out and, once they are interpreted, returns to the original document. In this way, word by word, most of the mystery words are deciphered, in this case by humans. “We are digitizing about 25 million words per day by having people type in captchas,” Dr. von Ahn said.

(Adapted from The New York Times, May 24, 2009)