The photo, which may have been taken in the early 1860s, was a testament to a dark part
of American
history, said Will Stapp, a photographic historian and founding curator
of the National Portrait Gallery's photographs department at the Smithsonian Institution.
"It's a very difficult and poignant piece of American history," he said. "What you are looking at when you look at this photo are two boys who were victims of that history.