Take a look at the above interactive to see how Christopher Oakley, a former Disney animator, pored over photographs of the dedication ceremony at the Soldiers' National Battlefield, where President Lincoln delivered the Gettysburg Address. There are three images of note, two made by noted Civil War photographer Alexander Gardner and one by David Bacharach.
The first screen details an identification of Lincoln made by John Richter, the director of the Center for Civil War Photography. Richter used two of Gardner's stereoscopic photographs (two identical images that, when seen together through a viewer, present a 3-D landscape) to identify a figure atop a horse as Lincoln. The right side of the second Gardner stereo view is seen in this screen; Oakley was able to obtain a high-resolution scan of the left side of this photograph, seen in the second screen.
This second screen, the higher-resolution version of Gardner's second stereo view, allowed Oakley to identify what he sees as Lincoln in a different location. He used a variety of sources, including an identification of Lincoln's secretary of state, William Seward, and a Lincoln portrait captured days earlier by Gardner, as a marker for seeking Lincoln. Oakley, who believes that Gardner assigned one of his associates to capture this stereo view, identifies Gardner in the foreground.
The third screen provides one of the sources used by Oakley to place the various members of Lincoln's "Team of Rivals"—his cabinet. In 1952, Josephine Cobb of the National Archives identified Lincoln in a photo taken by David Bachrach. It was considered to be the only image of Lincoln at Gettysburg until Richter made his identification 55 years later.