The best site I've come across on the web for public domain images, and very little chance that they aren't in the p.d. and you'll get sued.

It's not so huge that you'll spend a whole morning looking for what you want and has images that other sites don't seem to have, like famous people and historical figures (US-oriented). Though its called 'clipart' it has loads of good photos.

Check it out at pdclipart.org.

If anyone knows any better sites, please let me know - I can't wait!