Book excerpt: Photographs are used as documents, evidence, and records every day in courtrooms, hospitals, and police work, on passports, permits, and licenses. But how did such usages come to be established and accepted, and when? What kinds of photographs were seen seen as purely instrumental and able to function in this way? What sorts of agencies and institutions had the power to give them this status? And more generally, what conception of photographic representation did this involve, and what were its consequences?