APA style makes use of an in-text author-date citation system. In-text citations usually include enough information to point a reader to the proper citation in the Reference List. Archival materials can be challenging in such a system, as a document's creator or date of creation are sometimes unknown. For this reason, most of the examples provided in the manual include additional information elements.
See the Publication Manual of the APA, especially the preamble to section 6.11.
The photograph of the Japanese sentry displayed here is from the William H. Sager China Marines Photograph Collection. In an APA-style in-text citation, you might cite it as follows:
(Sager, W. Japanese Sentry, Hankow, [ca. 1945])
See Publication Manual of the APA, 6.11-6.21.