Online Resources for Public Domain Images:
*= extensive materials available.
*Time/Google Life Photo Archive: 10,000,000 LIFE magazine photographs searchable through Google.
*Pixabay.com: thousands of free use images. (Site located by Nikota S.)
*publicdomainpictures.net: thousands of free use images. (Another site located by Nikota S.)
*imagesafter.com: Hi resolution images, textures and photos
*Morgue File: A website with post production images made available for public use. Nice search capability.
*Getty Images: A huge online repository of images, many royalty free, with search capabilities.
*http://memory.loc.gov/ - U.S. Library of Congress digital image archive. (Some images are still under copyright, so caveat emptor.)
*Flickr.com- An online community of people sharing their photographs. Some images are available for modification in an educational setting. Many, however, a copy protected, check to make sure you can use the picture (look for an "ALL SIZES" button above the picture in question) and that you actually saved the work and not a tiny little 2-pixel picture.
*Amazing Textures- Large selection of tiles and textures in the public domain.
Big Foto- searchable database of Royalty Free pictures.
Aarin Free Photos- 950 Royalty Free pictures.
AMG Media- A small selection of public domain images, some wacky.
Art Favor- A small collection of public domain images, clipart and sounds.
Agricultural Research Service- Searchable database of agriculture-oriented photographs in the public domain.
Shorpy.com: An extensive archive of old photographs, many scanned from glass plate negatives.
Burning Well- An online repository of images placed into the public domain.
Creating Online- An online forum based collection of public domain images.
Cepolina Photo- An online album of 3500 downloadable photos.
Free Digital Photos: Free photographs intended for use by web developers and graphic designers.
http://www.firstgov.gov/Topics/Graphics.shtml - A portal to US Government images and photos. "Most of these images and graphics are available for use in the public domain"
http://pictures.fws.gov/ - U.S. Fish and Wildlife Service pictures
http://images.fws.gov/ - More U.S. Fish and Wildlife Service imagery
http://www.photolib.noaa.gov/ - NOAA Photo Library
http://images.usace.army.mil/ - United States Army Corps of Engineers Digital Visual Library
http://photolibrary.usap.gov/ - Antarctic Photo Library
http://www.usda.gov/oc/photo/opchomea.htm - USDA Online Photography Center
http://photogallery.nrcs.usda.gov/Index.asp - USDA Natural Resources Conservation Service Photo Gallery
http://www.history.navy.mil/branches/nhcorg11.htm- Department of the Navy - Naval Historical Center Photographic Section
http://www.defenselink.mil/multimedia/ - Current Department of Defense publicly released images.
David Rumsey Map Collection: A large online collection of maps, including many old and rare maps, all in the public domain.