Art: Exactly What Is a Photograph?

One of the most eye-haunting images in the big retrospective of 195 photographs by Harry Callahan is called simply Eleanor, Chicago, 1949. It is the broad, pale face of a big-jawed woman—in fact, Callahan's wife, Eleanor Knapp—rising from Lake Michigan. Her eyes are closed. Her dark hair, parted in the middle, falls in thick ropes that swash in the water. Because the body is hidden by the murky wavelets, the head has a dreaming, apparitional quality, a look reinforced by the waving tendrils of hair. Yet nothing about the photograph invites one to read it as a narrative of emotion. The...