MLA
Cowper, Leslie. Portrait of Gordon Stastton, Wearing a Suit. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 70. https://digital.library.emory.edu/purl/573bzkh1cz-cor.
APA, 6th edition
Cowper, L. Portrait of Gordon Stastton, wearing a suit (Box 70) [Photographic postcards]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/573bzkh1cz-cor.
Chicago
Cowper, Leslie. “Portrait of Gordon Stastton, Wearing a Suit.” Photographic postcards. Robert Langmuir African American Photograph Collection, n.d. Box 70. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/573bzkh1cz-cor.