In 1863, President Abraham Lincoln stirred the soul of an embattled nation with the famous speech he delivered in Gettysburg, Pa. And now, 150 years later, Lincoln has again aroused passions by being spotted — possibly — in a stereoscopic photograph taken on the day of the Gettysburg Address.

But is Abe Lincoln really in the photo? And, if so, which of two images of a bearded man in a black stovepipe hat is Lincoln? These questions have set off a dust-up in the normally staid world of archival photography, according to Smithsonian magazine.

Six years ago, John Richter, an amateur historian and director of the Center for Civil War Photography, magnified a stereograph taken by photographer Alexander Gardner on the day of Lincoln’s now-famous Gettysburg speech. Richter identified a tall figure on horseback, wearing a stovepipe hat and saluting the troops, as the 16th U.S. president.