Franking machine and method of forming franking impression

摘要

A method of forming a franking impression on a mail item and apparatus for forming the franking impression is disclosed. Material which is switchable from one stable state to another stable state by exposure to light of predetermined wavelength is deposited on the mail item while in one state and a selected region of the deposited material is exposed to light of the predetermined wavelength to effect switching of the selected region to the other state and thereby to represent franking or other secure information.