MLA
Valentine, and Sons. John Brown's Monument, Adirondacks, N.Y. 1907. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 69. https://digital.library.emory.edu/purl/0171vhhmkq-cor.
APA, 6th edition
V., & S. (1907). John Brown's Monument, Adirondacks, N.Y. (Box 69) [Photographic postcards]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/0171vhhmkq-cor.
Chicago
Valentine, and Sons. “John Brown's Monument, Adirondacks, N.Y.” Photographic postcards. Robert Langmuir African American Photograph Collection, 1907. Box 69. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/0171vhhmkq-cor.