All of the armed forces maintain publicly accessible photo files where you can find some great stock images for Veterans Day, Memorial Day, etc.

The United States Army, in particular, identifies their photos as being in the public domain:

Images on the Army Web site are cleared for release and are considered in the public domain. Request credit be given as “Photo Courtesy of U.S. Army” and credit to individual photographer whenever possible.

Here are a couple of great examples I found:

The Greatest Generation. Photo by Air Force Staff Sgt. Suzanne Day.

Where Valor Rests. Photo by Lt. Col. Michael Edrington.

For more, visit:

• Department of Defense: Photos
• Army: Photos
  
• Air Force: Photos
• Air Force: Art
• Navy: Photos
• Navy: Logos and Graphics
• Marines: Photos
• Coast Guard: Photos
• Coast Guard: Logos and Graphics
• Coast Guard: Art

Related Articles:

• 6 Sets of Photoshop Brushes of Military Vehicles, Aircraft, and Soldiers
• Vector Seals of the Army, Air Force, Navy, Marines, Coast Guard, and More
• Official Veterans Day Posters