The market for fine-art photography, an estimated annual $200 million slice of the art business, is bedeviled by a curious paradox. The medium itself tends toward iconic democracy: from one negative hundreds of prints can be made, all identical if need be and, in theory, of equal value. A print from the work "Noire et Blanche" by Man Ray. Some of Ray's images were faked by a forger exploiting collectors' desires for vintage prints. "Truck and Sign," 1930, by Walker Evans, is among the artist's photographs currently on view at the Metropolitan Museum, center.