What sites do you use to find public domain images?

I'm thinking of participating in this round of the_lj_reboot. I wanted to do something non-fandom based but I'm a bit stymied at finding images. I searched first for "royalty free," which led me to Getty but that isn't the same as "fee free." Then I searched for "stock photos" and ended up at another one-time-fee site. I searched for public domain images, ended up at Wikipedia's list of public domain resources but the four links I tried seemed to spit me out onto other Google results pages when I tried to search them.

I've been assuming all along that stock icon makers are accessing images that are placed into the public domain since I kind of doubt that they're paying for all those images they're turning into icons. (That could be a very expensive habit!)

I've been violating copyright left and right in making icons but I'd really like to do this layout on the up and up. However, I'm not so determined to do a non-fandom layout that I'll pay for images I might or might not end up using. This is a personal exercise and I'll happily turn it into an exploration of Daniel's glasses or Janet's Hairstyles if need be. ;-)