Methods and apparatus for spectrally-encoding plural source images and for providing the spectrally-encoded plural source images in a composite image, for rendering the composite image on a substrate, or for recovering at least one of the encoded source images from the rendered composite image such that the recovered source image is made distinguishable. The rendered composite image includes at least a first source image that is encoded and rendered with use of a selected colorant so as to be visually discernible on the substrate during a plurality of modes of intended illumination as a "background" image, and a second, "narrow band" source image that is encoded in the composite image so as to be recovered when illuminated by at least a selected of the plurality of modes of intended illumination that employs complementary narrow band illuminant.