One puzzle, called Gimpy, consists of a display of seven distorted, overlapping words chosen at random from a dictionary of simple words. Solving the puzzle requires identifying three of the seven words and typing them into the box provided. The Carnegie Mellon group also created a simplified version of Gimpy a single distorted word displayed against a complicated background. It is now part of Yahoo's registration process.
Another Captcha, called Sounds, consists of a distorted, computer-generated sound clip containing a word or sequence of numbers. To solve the puzzle, a user must listen to the clip and type the word or numbers into the box provided.
Sara Robinson, "Human or Computer? Take This Test," The New York Times, December 10, 2002
Blum's research team at Carnegie Mellon University has come up with a solution to the problem, one that the Web portal Yahoo implemented last month. Now, when computer users try to register with Yahoo, they must pass a test to verify that they are human, not a robot.
The test is administered by a computer program.
"Here you have a computer program that creates a test, administers it and grades it, but can't pass its own test," Blum said.
It's what Blum calls a "captcha," a "gotcha"-inspired acronym that means Completely Automatic Public Turing test to tell Computers and Humans Apart.
The captcha is based on the fact that people can easily analyze images that flummox computers. For the Yahoo site, new registrants must read a common word that has been twisted or distorted and then type it into a box. It's easy for humans; impossible for computers.
Byron Spice, "Robot solves Internet robot problem," Pittsburgh Post-Gazette, October 21, 2001
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