in reply to Re^4: If CAPTCHA isn't the answer. What is?
in thread If CAPTCHA isn't the answer. What is?

Than can be easily prevented by requiring that the user selects not "The three cats among these 9 images" but "All cats among these images" (there can be more or less, even none!) or maybe "The second brown cat and the last dog".

--
David Serrano

  • Comment on Re^5: If CAPTCHA isn't the answer. What is?

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Re^6: If CAPTCHA isn't the answer. What is?
by ikegami (Patriarch) on Aug 02, 2006 at 17:17 UTC

    Indeed 

    1/10 * C(9,0) +
1/10 * C(9,1) +
1/10 * C(9,2) +
1/10 * C(9,3) +
1/10 * C(9,4) +
1/10 * C(9,5) +
1/10 * C(9,6) +
1/10 * C(9,7) +
1/10 * C(9,8) +
1/10 * C(9,9) = 1/10 * 2 * (1 + 9 + 36 + 336 + 4536)
              = 983.6

    [download]

    1 in 84 becomes 1 in 983.6

    On the other hand, it makes it harder on the user. People will be second guessing themselves.

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