MLA

Simpson, Randolph Linsly, 1927-1992. Unknown photographer Full length formal portrait, soldier seated facing left. Photographic postcard. Box 25. circa 1918. https://collections.library.yale.edu/catalog/2042479.

APA, 6th edition

Simpson, Randolph Linsly, 1927-1992. (["Box 25"])(circa 1918)[Unknown photographer Full length formal portrait, soldier seated facing left. Photographic postcard]. https://collections.library.yale.edu/catalog/2042479.