1. A method of processing a plurality of source images, comprising the steps of: encoding the plurality of source images in a composite image, wherein multiple-illuminant GCR is employed to alter to the composition of one or more source images encoded for rendering as a composite image; rendering the composite image on a substrate by use of a plurality of colorants; and recovering at least one of the encoded source images from the rendered composite image, such that the recovered source image is made distinguishable, by subjecting the rendered composite image to a narrow-band illuminant that is preselected to reveal the source image.