Cite

[Indian man standing next to a White man on a horse]

MLA

Hillers, John K. [Indian Man Standing next to a White Man on a Horse]. 0AD. https://collections.library.yale.edu/catalog/2018205.

APA, 6th edition

Hillers, J. K. (0 C.E.). [Indian man standing next to a White man on a horse] [Photographic prints, Photographs]. https://collections.library.yale.edu/catalog/2018205.