The present invention is a process of producing a decorated case insert suitable for use on a phone or tablet that applies a synthetic organic polymer coating onto a heat stabilized extruded polymeric substrate, and diffuses a set of disperse dyes in the form of an image into the polymer applied coating through the application of heat and pressure. The decorated insert is then cut to match an article or manufacture, such as a phone or tablet case, and affixed onto that case to form a decorated case.