1. An image forming medium, comprising a substrate; and an imaging layer coated on or impregnated into said substrate, the imaging layer comprising: a photobase generator, a coupling agent, and a photoacid generator, wherein: the photobase generator and the coupling agent are selected so that irradiation of the imaging layer with light of a first wavelength causes said photobase generator to generate a base that reacts with the coupling agent to produce an extended conjugation that forms an image, the photoacid generator is selected so that irradiation of the imaging layer with light of a second wavelength causes said photoacid generator to generate an acid that reacts with the extended conjugation to reverse formation of the extended conjugation to erase the image, and the first wavelength is different from the second wavelength.