MLA
Spencer, Thomas. M. M. Keys of Cartersville, Georgia. Keys Saw the Remains of Abraham Lincoln in Indianapolis, Indiana on April 30, 1865 during the Transportation of Abraham Lincoln's Body from Washington, D.C. to His Hometown of Springfield, Illinois. 1940. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 16, Folder 43. https://digital.library.emory.edu/purl/4579s4mww2-cor.
APA, 6th edition
Spencer, T. (1940). M. M. Keys of Cartersville, Georgia. Keys saw the remains of Abraham Lincoln in Indianapolis, Indiana on April 30, 1865 during the transportation of Abraham Lincoln's body from Washington, D.C. to his hometown of Springfield, Illinois (Box 16, Folder 43) [Black-and-white photographs]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/4579s4mww2-cor.
Chicago
Spencer, Thomas. “M. M. Keys of Cartersville, Georgia. Keys Saw the Remains of Abraham Lincoln in Indianapolis, Indiana on April 30, 1865 during the Transportation of Abraham Lincoln's Body from Washington, D.C. to His Hometown of Springfield, Illinois.” Black-and-white photographs. Civil War Collection, 1940. Box 16, Folder 43. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/4579s4mww2-cor.