DOCUMENTS WITH SECURITY MARKINGS

摘要

A security-marked document 10 carries an image in reversibly colour-changeable photochromic or thermochromic print and also carries an image in constant-colour print. An apparatus for reading the security markings comprises means (e.g. UV light 34) for acting upon the document to change the colour of the photochromic print, and means (e.g. camera 30) for viewing the document after the colour-change and to form electrical signals representing the image being viewed, so that the document can be verified. These image-representing signals may be compared with corresponding signals obtained by viewing the document before the colour-change is effected. The colour-changeable print and the constant capture colour print may be in encoded form. A keyboard 40 may be used to input a PIN code into the image processing unit 32.