1. A biometric measurement system comprising: a platen; a thin film; an illumination source disposed to illuminate a skin site positioned over the platen in a configuration in which the thin film is disposed between the platen and the skin site; an imaging system disposed to receive light scattered from the skin site; and a controller interfaced with the illumination source and the imaging system, the controller including: instructions to illuminate the skin site through the thin film under a plurality of distinct optical conditions during a single illumination session; instructions to derive an image of the skin site from light received by the imaging system with direct imaging according to the distinct optical conditions; and instructions to perform a biometric function with the derived image.