Image*After: Large collection of free stock images and textures that may be modified and re-used for personal and commercial projects
The Commons by Flickr: Images from archives, museums, libraries and research centers such as the New York Public Library, Smithsonian, Library of Congress and Getty Research Institute. The images have no known copyright restrictions.
stock.XCHNG: Free stock images, powered by Getty Images
Clip Art History: Free high-quality public-domain clipart covering all ages of world history. Images may be used for any purpose
Public Domain Clip Art: Large collection of public domain clip art. Images may be used for any purpose and registration is not required