MLA
Happy as the Day Is Long : an African American Boy in a Hat Sitting on a Ledge. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 72. https://digital.library.emory.edu/purl/180vq83bmk-cor.
APA, 6th edition
Happy as the day is long : an African American boy in a hat sitting on a ledge (Box 72). [Postcards]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/180vq83bmk-cor.
Chicago
“Happy as the Day Is Long : an African American Boy in a Hat Sitting on a Ledge.” Postcards. Robert Langmuir African American Photograph Collection, n.d. Box 72. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/180vq83bmk-cor.