Security document with positive and negative authentication tilt images
AssigneeMorpho
InventorsJan Van Den Berg, Erik Van Dijk
Life of this patent
Estimating the term…
Abstract
Disclosed is a security document including an image layer with in a first image area an identification image. The document has in a second image area an authentication image that is composed of a first authentication image that is a positive version of the first image and a second authentication image that is a negative version of the first image. The authentication images can be observed at different angles and form a tilt image. Mutual comparison of the positive and negative tilt images and comparison with the identification image provides improved detection of unauthorized alterations.
Claims5
A method of providing a security document (1), comprising steps of:
- providing an image layer (2) with an array of cylindrical lenses (10);
- providing an image processing unit (18) with an identification image having image elements with predetermined brightness values (Bp) on a positive brightness scale;
- providing the image processing unit (18) with a positive authentication image (7) corresponding to the identification image (4) with picture elements having brightness values that correspond to brightness values of the identification image (4), and a negative authentication image (8) corresponding to the identification image and with picture elements having brightness values (Bn) that correspond to a reversed brightness scale in which brightest one of the picture elements in the positive brightness scale appear darkest and darkest one of the picture elements appear brightest;
- and
- laser engraving the positive authentication image (7) and the negative authentication image (8) through the cylindrical lenses (10) in the image layer (2) at first and second angles (α1, α2), respectively, such that both the identification image (4) and the first authentication image (7) are observable at a perpendicular viewing direction, and the second authentication image (8) is observable at a non-perpendicular viewing direction.
Dependencies are inferred from the claim text.