1. Wikipedia

Check under the image for credit information. In addition, they have a site that lists other public domain websites.

2. Stock.xchng

Easy-to-use, many images available. Generally free images, high quality. Usually you
must write the photographer and wait for a response, but we have gotten responses
quickly.

3. Library of Congress Prints & Photographs Online Catalog

Not all images are in the public domain, most are and it is stated when they are not. Also,
not all images are digitally available, even if there is a thumbnail present. This is an
excellent source for historical photos, especially American history. It is also a good
source of historical illustrations.

4. The U.S. Department of State

Lots of good images of recent/current politicians. Most of the images are in the public
domain, and are copyright free unless noted.

5. NASA

“NASA still images, audio files and video generally are not copyrighted. You may use
NASA imagery, video and audio material for educational or informational purposes,
including photo collections, textbooks, public exhibits and Internet Web pages."
Images of aircraft, space telescope images, weather, earth from space, planets, etc.

6. U.S. Army Corps of Engineers Digital Visual Library

Photos of Corps projects from around the world.

7. USDA Photography

Pictures of agriculture, produce, workers, and Farm Security Administration photos from
the 1930's and 1940's.

8. U.S. Navy Photography

All images are in the public domain, can be freely downloaded and used for any purpose.
Ships, aircraft, ports, people. Images of speakers at Naval events (politicians, etc.)

9. National Archives site for "100 Milestone Documents"

This is where we obtained the original copies of the Constitution, the Bill of Rights and
the Declaration of Independence. It also has many other valuable documents pertaining to
U.S. history.

10. The White House

Photo essays of White House events, speakers, politicians, etc.

11. The Associated Press Image Archive via Accuweather.com

Must click "search" to enter Accuweather AP website.
From simple keyword searching to more complex searches such as
concept, color, and category, research projects are enhanced with the
diversity of subject matter contained within the Archive. Over two million
photographs dating back to 1826, more than one million audio sound bytes
dating from the 1920's, two million Associated Press news stories from
1997, and a professionally produced collection of more than 45,000 maps,
graphs, charts, logos, flags, illustrations, etc. are included. Updated with
more than three thousand photos daily, the Archive is licensed for
educational use exclusively through AccuWeather, Inc.

12. The Defense Visual Information Center

Mostly military images, some civilian/celebrities. Good for politicians. All high quality.

13. Defense Link

Mostly military images, etc.