MLA

Simpson, Randolph Linsly, 1927-1992. Unknown photographer White man in shirt, bowtie, hat sits on porch steps; black child seated between his knees. Photographic postcard. Box 26, folder 1047. circa 1920. https://collections.library.yale.edu/catalog/2057837.

APA, 6th edition

Simpson, Randolph Linsly, 1927-1992. (["Box 26, folder 1047"])(circa 1920)[Unknown photographer White man in shirt, bowtie, hat sits on porch steps; black child seated between his knees. Photographic postcard]. https://collections.library.yale.edu/catalog/2057837.