[Abraham Lincoln on battlefield at Antietam, Maryland, cropped version that highlights McLellan and Lincoln]

Abraham Lincoln with, from left: Col. Alexander S. Webb, Chief of Staff, 5th Corps.; Gen. George B. McClellan; Scout Adams; Dr. Jonathan Letterman, Army Medical Director; an unidentified person; and standing behind Lincoln, Gen. Henry J. Hunt.
Ostendorf, no. 62 (variant)
Meserve, no. 44
Published in: Lincoln's photographs: a complete album / by Lloyd Ostendorf. Dayton, OH: Rockywood Press, 1998, p. 400 and 107.

Alexander Gardner (October 17, 1821 - December 10, 1882) was a Scottish photographer who is best known for his photographs of the American Civil War. He emigrated to the United States in 1856 and worked as a photographer in Mathew Brady's studio. Gardner was sent to document the American Civil War and produced some of the most iconic images of the conflict, including photographs of the battlefields at Antietam and Gettysburg. After the war, Gardner photographed President Lincoln and the American West, including images of Native Americans, settlers, and the construction of the transcontinental railroad.