Authentication can be fun remaindered a link to this article from Microsoft Research proposing to use inkblots for authentication (identifying users online). It reminds me a bit of another authentication scheme called Passface, now called Real User, which identified users by having them pick out a series of faces from a larger set of faces. Both capitalize on quirks of human perception to create more secure authentication schemes.
They're fun and potentially more effective than using simple text and numeric string passwords, but I find they take too long and end up being too much trouble to gain widespread adoption. I don't want to have to step through a series of pages, identifying ten inkblots or a series of faces, just to log in to a website. Sure, that's lazy, but entire empires have been built on human laziness.