I love it when people do fun new things with code. This is a really fun hack that was done some time ago that I stumbled across today and thought I would share it.
All you need is knowledge of Perl (take some anti-depressants and watch the videos below) a little creativity and an image manipulation library.
I am certain that similar things can be done with Gimp and Scheme or Python. I'm sure I'll come across something worthy of posting eventually.
If you go in for this kind of thing and you're into Java - I should point out that Processing recently released the 1.0 version. I have been toying with pre-release versions of Processing for about a year now. It's deeeeep man.