I've seen similar systems, such as "Which one of these four images is a puppy?". I think the problem is that the set has to be small, so it ends up being a multiple choice quiz. With one correct answer out of four or five choices, it is very easy to brute force.
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I've often thought captchas were doing it wrong.
Even my pre-school self could solve the Sesame Street "one of these things is not like the other".
There are so many sets with an odd-one-out that would only be easily determinable by a human over a computer.
I've seen similar systems, such as "Which one of these four images is a puppy?". I think the problem is that the set has to be small, so it ends up being a multiple choice quiz. With one correct answer out of four or five choices, it is very easy to brute force.
The ones I've seen don't ask you to identify one single puppy. They ask you to identify all the puppies, making it rather harder to brute force:
http://thepcspy.com/read/the_cutest_humantest_kittenauth/
http://research.microsoft.com/en-us/um/redmond/projects/asir...