Abstract:
A method of producing a digital multiple-level encoded image (Fig. 7) is presented. The method comprises obtaining a digital authentication image (S110), obtaining a first encoding parameter set (S115) comprising one or more encoding parameters, and constructing a first encoded image (S125). The first encoded image is constructed using a first encoding methodology, the digital authentication image and the first encoding parameter set. The method further comprises obtaining a second encoding parameter set (S130) comprising one or more encoding parameters and constructing a second encoded image (140) using a second encoding methodology, the first encoded image and the second encoding parameter set. The second encoded image may be decoded to reveal the first encoded image using a decoder having characteristics corresponding to at least a portion of the encoding parameters of the second encoding parameter set. The first encoded image may be decoded to reveal the authentication image using a decoder having characteristics corresponding to at least a portion of the encoding parameters of the first encoding parameter set.
Abstract:
A document containing security images which enable original documents to be distinguished from copies of the originals. The document may include a background of a first color and an image formed of a second and third color which appear to be the first color when viewed together, providing a hidden image which does not appear in reproductions of the document. The document may contain a background of a first color printed with lines at a first angle, and an image of the first color but having lines printed at a different angle, providing a hidden image which does not appear in reproductions of the document. The document may contain a background of printed with lines at a first angle and a predetermined line frequency, and an image printed with lines at a second angle and at a line frequency less the one half of the line frequency of the background, providing a substantially hidden image which appears in a reproduction of the document. A document may be authenticated as an original document by detecting the presence of a predetermined hidden security image and/or by determining the layout of the document to be the same as the expected layout of an original document.