Since its earliest days, photography has been practiced by thousands who shared no common tradition or training, who were disciplined and united by no academy or guild, who considered their medium variously as a science, an art, a trade, or an entertainment, and who were often unaware of each other’s work... Some of these pictures were the product of knowledge and skill and sensibility and invention; many were the product of accident, improvisation, misunderstanding, and empirical experiment. But whether produced by art or by luck, each picture was part of a massive assault on our traditional habits of seeing.