MLA

Man Addressing Students Outdoors While Another Draws on a Chalkboard, South Africa, Ca. 1920-1940. 1920. https://collections.library.yale.edu/catalog/11447293.

APA, 6th edition

Man addressing students outdoors while another draws on a chalkboard, South Africa, ca. 1920-1940. (1920). [General views (AAT), photographic postcards (AAT), photographs (AAT)]. https://collections.library.yale.edu/catalog/11447293.