A few months back I started posting more images here as they make the blog look better and more readable.
Here’s where I get most of the images for Polizeros.
Commons.wikipedia.org has over 2 million “freely usable” media files. A huge and helpful resource.
The Library of Congress new project, The Commons on Flickr.
Clipart.com. $159 a year. Download as many as you want. “8,000,000 clipart images, photos, illustrations, animations, fonts and sounds.”
Stockxpert.com “Royalty free stock photography,” and lots of it, all pro quality. Unique pricing structure as you can pay per photo, and prices (for the size photo you’ll need on the web) are a mere $1 each.
Wikipedia (where else) lists dozens of public domain images resources. Lots of good stuff here too, haven’t had time to go through all of them.
You’ll probably need to edit or tweak the images.
GIMP. Open source, multi-platform, and free. Unless you are a true Photoshop wizard, GIMP will probably do all you’ll ever need, even if the interface is a bit quirky.
Feel free to add resources in the comments.