An Interesting free source

Wikimedia is an interesting source of free images. If you are not up on the copyright / copyleft arguments , the media on this stuff does not have copyright so can be used as you want - actually it isn't that simple but look at the site and see what they have.

In their own words

Wikimedia Commons is a media file repository making available public domain and freely-licensed educational media content (images, sound and video clips) to everyone, in their own language. It acts as a common repository for the various projects of the Wikimedia Foundation, but you do not need to belong to one of those projects to use media hosted here. The repository is created and maintained not by paid archivists, but by volunteers. The scope of Commons is set out on the project scope pages.