MLA
Spencer, Thomas. Ruins of Best Mill in Georgia. The Mill Was Destroyed by Union Troops in 1864. 1940. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 15, Folder 2. https://digital.library.emory.edu/purl/3720cfxqrs-cor.
APA, 6th edition
Spencer, T. (1940). Ruins of Best Mill in Georgia. The mill was destroyed by Union troops in 1864 (Box 15, Folder 2) [Black-and-white photographs]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/3720cfxqrs-cor.
Chicago
Spencer, Thomas. “Ruins of Best Mill in Georgia. The Mill Was Destroyed by Union Troops in 1864.” Black-and-white photographs. Civil War Collection, 1940. Box 15, Folder 2. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/3720cfxqrs-cor.