cognition required

after some discussion in mark pilgrim's comments about user entry systems that require a person to read an image (in the interest of preventing computers from entering), accessibility guru joe clark admits Even the suggestions I made for password-verification systems aren?t so hot. this doesn't strike me as a particularly difficult problem to solve. existing systems typically rely on the ability of a person (and the inability of a computer) to see. a better system, one accessible to the blind, would rely on the ability of a person (and the inability of a computer) to think. randomly generate a sentence with a simple pattern that a child could read and understand, such as: "tom's coat is big and brown." change the names, objects, sizes, colors, and even sentence form every time. then ask a simple question: "what color is tom's coat?" not only will this be a (blind) human-accessible and computer-inaccessible system of entry, but it will also - as an added bonus - push funding of spam towards computer cognition research.

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knows half of 8 is