1. A method of processing a plurality of source images, comprising the steps of: encoding the plurality of source images in a composite image, the plural source images including at least a first source image that is encoded so as to be a background image having image content that is visually discernible on the substrate during a plurality of modes of intended illumination, and a second source image that is encoded so as to be a narrow band image having image content that is visually discernible on the substrate during a single mode of intended illumination; rendering the composite image on a substrate by use of a plurality of colorants; and recovering the first and second encoded source images from the rendered composite image, such that the recovered first and second source images are made distinguishable by subjecting the rendered composite image to a narrow-band illuminant that is preselected to reveal the second source image, and such that the image content of the second source image is discernible and thus achieves visual prominence with respect to the first source image.