xtom - 9:34 pm on Jun 20, 2007 (gmt 0)

I like the captcha alternatives which go something like this: Robert's brother Tom has a son named Mark Woodford. What is the full name of Mark's uncle? Can computers figure that sort of thing out? If so, how?

Trouble with questions like that is that they would be too hard for real users to answer quickly. It's almost like a riddle.