CoolToolsfor21stCenturyLearners has put together this list of sources of photos that are copyright friendly - i.e. images that your kids can use without worrying they're breaking copyright law by cutting and pasting the images they find on the web.
Interesting piece of research this! I can't watch the needle going in anyway - the whole piercing my skin thing just creeps me out! - but here's a good reason I can give now!