1. Wahington Crossing the Delaware
Prior to the invention of photography, and then the American Civil War, images of warfare were usually allegorical representations of the glory of battle. Emanuel Leutze's famous painting of Washington had very little in common with actual events during the Revolutionary War. Occasionally, artists used their work, to to glorify war, but to condemn it. For instance Goya's Execution of the Rebels, and Picasso's Guernica. But again, these paintings are more about composition and style than depicting reality.
2. Mathew Brady
Timothy O'Sullivan began his career as an apprentice to Mathew Brady. Brady was a world class portrait photographer raised in the art community and especially influenced by the artist William Page, Brady yearned to create great art, but photography had not yet attained a level of respect in the art world. Brady himself felt photography was inferior to the classical arts. In order to justify the importance of his work, Brady aspired to record history as it happened. He photographed all of the greatest leaders of the time.
3. Bull Run
Then the war broke out. In 1861 Brady assembled a group of assistants, including O'Sullivan, to travel with him to the battle of Bull Run in order to photograph a more extreme case of history in the making. The experience was harrowing for Brady and he never went out into the field again. He was, however, dedicated to capturing images of the war. Brady assigned traveling darkrooms to a selection of his assistants and sent them out into the field with the military, while he stayed in New York and continued making portraits.
Of Brady's assistants, Timothy O'Sullivan, along with Alexander Gardner, was the most successful. O'Sullivan had slightly different aspirations than his employer. While Brady wanted his work to be artistically important, O'Sullivan was arguably the very first photojournalist. He captured events exactly as the appeared in front of him with little or no interpretation. He never attempted to manipulate the viewer using the traditional tools of the artist. His compositions are almost always straightforward, and he never altered the scene to make it more appealing than it was in reality.
5. The Moved Body
O'Sullivan's colleagues, on the other hand, were not above viewer manipulation. Most notoriously, the famous works of Alexander Gardner, A Sharpshooter's Last Sleep and Home of a Rebel Sharpshooter are suspected of major alteration. The rifle seen in the photos was not Confederate regulation and is thought to have been a prop included by Gardner. The bodies seen in the photos are also in question. Researcher's claim that both photographs depict the same dead soldier. This implies that Gardner actually moved and posed the body into position for multiple shots