An image forming medium includes a substrate, and an imaging layer coated on or impregnated into the substrate, wherein the imaging layer includes a photochromic polymer, optionally dispersed in a polymeric binder or a phase change binder, the photochromic polymer including a polymer having at least one photochromic unit grafted therein, wherein the imaging layer exhibits a reversible transition between a colorless state and a colored state in response to heat and light and wherein the imaging layer does not exhibit a transition from the colored state to colorless state when heated in the absence of light.