There are well over two dozen options, and the randomness is applied each time a browser requests it - so not only does it change each time, but that selection is also independent for each person; tell your browser to refresh, and it will change. The implementation is only a couple of lines in the Apache configuration file, as there is a built-in function for the purpose! When I fancy a new avi, I just add it to the list, which is now around three dozen (and there are a few others I have removed as well). Because they all have to be the same type, and I happened to choose jpg not gif or png when I set it up, there can't be any dynamic ones - which is fine by me. I do the same at PocketJury, but the list is smaller (for my own reasons).
Here, there are pictures of me at all ages, my pets at various times (five dogs and a horse), a house-sized graffito in Hackney (East London), some other photos I have taken, a couple of Jeph's doodles (cat, frog, and one from QC), Johann from Anders Loves Maria, Shinji from Evangelion, Kintaro Oe from Golden Boy, and (the largest number) Scott Pilgrim - not all from the books, some are from convention sketches. It generally seems to be the Scott Pilgrim ones that are most directly expressive of a simple mood, which is why there are the largest number of them, and also why they seem to give most of the post/avi coincidences that are pleasing (Shinji works quite well, too).
