A method of security printing can comprise the steps of printing a transparent ink onto a portion of a coated substrate resulting in printed region and an unprinted region, where the transparent ink is devoid of dyes, pigments, ceramics, metallics, and fluorescents; illuminating both the printed region and the unprinted region of the substrate, where the printed region scatters more light than the unprinted region creating a contrast; and detecting the contrast with a sensor that is sensitive to detecting light scattering differences between the printed region and the unprinted region.