In order to meet the strict requirements of filming at a National Historic Site, the production could not use the state box on the right side of the stage where President Lincoln was actually shot as it contained authentic relics from the assassination. Fortunately, the opposite side of the stage was identical. To solve this problem, Courtney and D.P. Ben Brunkhardt chose to film into a mirror. Together, large format camera company iWERKS and Camera Asst. Fred Wiegel engineered a front-surfaced mirror and mounting rig that stabilizes a reversed image. In order to ensure the film's authenticity, this meant everything from Booth's shooting hand to Lincoln 's mole needed to be reversed.