Gardner was a Scottish photographer who later moved to the United States and became a staff photographer for the commander of the “Army of the Potomac.” This prominent war photographer had photographed the “Battle of Antietam,” “Battle of Gettysburg,” “Battle of Fredericksburg” and other important battles that changed the course of history. He is best known for his photographs of the American Civil War, U.S. President Abraham Lincoln, and the execution of the conspirators to Lincoln's assassination.