One of the more common analogies in archival literature is that comparing archivists to detectives. But even Sherlock Holmes, the "most perfect reasoning machine the world has ever seen" (in the words of his biographer, Dr. Watson), might quail at the task facing an archivist who must identify and date photographs in twentieth century political collections. Bereft, in most cases, of the technological clues that enable those working with nineteenth century photographs to date by photographic process, the archivist faces a situation that, in the words of Canadian archivist Richard J. Huydra:
"presents numerous fundamental difficulties. Existing captions are of ten incomplete, inaccurate, deliberately distorted or irrelevant. For photographs with no captions, the task of identification is even more difficult. Recognition by memory or through comparison with other visual evidence is often inadequate and unreliable."