The School of Education at the University of North Carolina has published an excellent introduction for students working on visual literacy by examining historical photographs:

In many photographs, information about the people, events, setting, and so on are made explicit by the photographer — there are distinct visual clues that tell us who the people are, what they are doing, and where and when the photograph was taken. In other cases, though, that information is implicit — implied but not clearly communicated by the photographer, or left to be inferred by the viewer. The identities of the people in the photograph may be unclear; their purpose may be unknown; the time and place may be difficult or impossible to discern. When the context is implicit, viewers are left to fill it in on their own, making assumptions based on their own experience or values. Viewers may not even realize that they are making those assumptions — we may fill in a photograph’s context without really thinking about it. (Reading Photographs)

Visual Literacy Activity:
Look carefully at the paired photos to the right.  Concentrating on the larger image, respond to these questions.   Cleveland News. Mar 8, 1908.