1. An optical fingerprint imaging system for acquiring fingerprint images, the imaging system comprising: an optically transparent platen having an exterior surface through which a fingerprint image is to be acquired; a protective film comprising urethane that is substantially free from imperfections that would affect transmission of light in acquiring a fingerprint image and which is substantially chemically inert to petroleum-based substances with which it may come into contact when receiving a finger to acquire a fingerprint image, the protective film having an outer surface and an inner surface, the inner surface facing the platen, the film adapted to resiliently deform to ridges of a fingerprint from a finger pressed onto the film; and an adhesive disposed on the inner surface of the protective film for removably attaching the protective film in optical alignment with the platen, the adhesive having a selected cohesive strength such that the protective film may be removed without leaving an adhesive residue thereby allowing repeated replacement of the protective film.