[z2amiller]

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.

[sedm0784]

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...