A visible light characteristic changing layer is formed in a location which can be viewed from a part of a label surface of an optical medium. The first movable part moves along a first direction. Only local references are used in the configuration of the nameservers and switches, and in the computation and signalling of the service and transport paths, respectively. The photodetector may be a Schottky contact or a p-n junction in a semiconductor. Corresponding electrophotographic apparatuses and imaging methods are described. The precoating is carried out by electroplating, by chemical or physical vapor deposition or by co-rolling.