Captcha the Puzzle

By Ivars Peterson, 15:52 PM April 15, 2008

Computers can do all sorts of amazing things, from searching the Web at an incredible rate to playing chess at a grandmaster level. Yet some tasks that are easy for people to perform remain remarkably difficult for computers. For example, computer programs have a hard time reading distorted text or deciphering images.

In the last few years, computer scientists have worked out an ingenious security scheme that takes advantage of such a mismatch. The scheme relies on computer programs that can,...

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