Pics4Learning is a copyright-friendly image library for teachers and students. The Pics4Learning collection consists of thousands of images that have been donated by students, teachers, and amateur photographers. Unlike many Internet sites, permission has been granted for teachers and students to use all of the images donated to the Pics4Learning collection.
Professional photographers seel their photos here. However, the usage agreement on the front page states: "Also non-commercial users may download our web size images to use off-line in school projects, church services, cards, leaflets, etc. Basically, if your off-line use is not commercial, you can download our web size images for free."
Smithsonian Images An AMAZING collection of photos on history and science. You must credit the Smithsonian and the photographer.
Library of Congress American Memory Collection
Library of Congress Prints and Photographs Online
New York Public Library Digital Collections
National Museum of American History
Gimp-Savy Community tagged photos from public domain sources, NASA, NOAA, FWS.
USA.gov Public domain photos from various government agencies.
Agricultural Research Service Search for images of animals, crops, insects, plants, etc.
National Oceanic and Atmospheric Administration Search for underwater images, coral reefs, weather, polar regions, coastlines, lighthouses, etc.
National Park Service Digital Image Archives- includes images from national parks, monuments, historic sites, and related areas. Searchable by park.
U. S. Department of Defense Images- hundreds of military photos
DK Clipart Images and clipart from Dorling Kindersly books that may be used in school projects and just for fun.
Stock.XCHNG http://www.sxc.hu/ Searchable database of photos freely usable for educational purposes.
YotoPhoto is a creative commons search site
MorgueFile is a site with creative commons images you may use without attribution.