What the moralists are demanding from a photograph is that it do what no photograph can ever do—speak. The caption is the missing voice, and it is expected to speak for truth. But even an entirely accurate caption is only one interpretation, necessarily a limiting one, of the photograph to which it is attached. And the caption-glove slips on and off so easily. It cannot prevent any argument or moral plea which a photograph (or set of photographs) is intended to support from being undermined by the plurality of meanings that every photograph carries, or from being qualified by the acquisitive mentality implicit in all picture-taking—and picture-collecting—and by the aesthetic relation to their subjects which all photographs inevitably propose.
— Susan Sontag, On Photography, 1977