Photographers covered the Civil War, following the Union Army in wagons that served as traveling darkrooms. Their equipment was bulky and the exposures had to be long, so they could not take action photographs during battle. But photography was graphic; this picture taken on the morning of July 4th, 1863 after three days of heavy fighting during the Battle of Gettysburg, showed the northern public that dying in battle lacked the gallantry often represented in paintings and prints.
Source: (Timothy H. O’Sullivan) Alexander Gardner, Gardner’s Photographic Sketch Book of the War, Vol. 1 (1866)—Prints and Photographs Division, Library of Congress.