Photographs are used as documents, records and evidence every day in courtrooms and hospitals, on passports and driving licences. But how did photographs come to be established and accepted, what sort of agencies and institutions have the power to enforce this status and, more generally, what concept of photographic representation is entailed and what are its consequences? In addressing such issues, John Tagg traces a previously unexamined history which has profound implications not only for the theory and practice of conventionally separated areas of amateur, professional, technical, documentary and art photography, but also for the understanding of the role of photography in processes of modern social regulation.