This is a picture of the Model 1898 eagle insignia worn by all American officers on the khaki uniform. For officers below the rank of Colonel, the eagles were worn on the shoulder straps between their rank insignia and the button securing the shoulder strap itself. Second Lieutenants only wore the eagles on the uniform's shoulder straps, since they had no rank insignia. For Colonels and higher, the eagles were worn on the collar of the uniform, replacing the letters "U.S." or "U.S.V." The eagles were worn so the eagle's beak faced the front of the wearer, hence on the eagle on the left was worn on the right side and the right one on the left. Actual size is only 1.25" in height, but this picture shows the exacting detail used for officers' uniforms.
U.S. Army Quartermaster Department, Regulations and Decisions pertaining to the Uniform of the Army of the United States, Second Edition, 20 June 1898, (Washington, Government Printing Office, 1898).