MLA
Mark, M. Old Slave Market, Where Slaves Were Formerly Sold at Auction, Erected 1840, St. Augustine, Fla. 1909. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 74. https://digital.library.emory.edu/purl/030prr4xjr-cor.
APA, 6th edition
Mark, M. (1909). Old slave market, where slaves were formerly sold at auction, erected 1840, St. Augustine, Fla. (Box 74) [Postcards]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/030prr4xjr-cor.
Chicago
Mark, M. “Old Slave Market, Where Slaves Were Formerly Sold at Auction, Erected 1840, St. Augustine, Fla.” Postcards. Robert Langmuir African American Photograph Collection, 1909. Box 74. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/030prr4xjr-cor.