Street photography has always operated in a zone of contested consent. The photographer moves through public space, makes images of people who did not agree to be photographed, and either publishes them or retains them as part of a body of work. The legal framework in most jurisdictions permits this — public space is public — but the legal permission resolves none of the ethical questions, which are more complicated now than they were when Cartier-Bresson was working in Paris in the 1930s.

The photo essay was a form. It had a grammar. A sequence of images, usually between eight and twenty, selected and ordered to carry a narrative or make an argument that no single photograph could sustain alone. It appeared in Life, Look, Paris Match, and later in the serious newspaper supplement magazines that proliferated through the 1980s and 1990s. It required an editor who understood sequencing, a photographer who thought in arcs rather than moments, and a reader who would sit with it for ten or fifteen minutes.

On Photography was published in 1977 and has not been out of print since. That fact alone suggests Sontag was doing something more than journalism. She was building a framework, and frameworks built well outlast the specific occasions that prompted them. Fifty years on, the book reads as both essential and incomplete — which is a more interesting verdict than either pure endorsement or dismissal. What Sontag got right was the fundamental argument about photography’s relationship to reality.