The edges of address elements such as address labels and window apertures located on a mailpiece, are detected by utilizing illumination from first and second alternating "on" and "off" light sources which illuminate the address elements at an acute angle. In the case of label detection, the edge closest...http://www.google.co.uk/patents/US4782238?utm_source=gb-gplus-sharePatent US4782238 - Apparatus for generating edge position signals for use in locating an address element on a mailpiece
