Security document with positive and negative authentication tilt images
AssigneeMorpho
InventorsJan VAN DEN BERG, Erik VAN DIJK
Life of this patent
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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.
Claims15
Security document (1) comprising an image layer (2) with in a first image area (3) an identification image (4) comprising picture elements with predetermined brightness values on a positive brightness scale, and in a second image area (5) an authentication image (6) corresponding with the first image (4), the authentication image (6) comprising at least two images (7,8) situated below lenses (10) such that at a first observation angle (α1), a first authentication image (7) is visible and at a second observation angle (α2), a second authentication image is visible (8), wherein the first authentication image (7) is a positive image corresponding with the first image (4) with picture elements having brightness values that correspond to the brightness values of the identification image and the second authentication (8) image is a negative image corresponding with the first image (4), with picture elements having brightness values that correspond to a reversed brightness scale that is obtained by making the brightest picture elements in the positive brightness scale appear darkest and making the darkest picture elements appear brightest, and wherein both the identification image (4) and the first authentication image (7) can be observed at a perpendicular viewing direction while the second authentication image (8) can be observed at a non-perpendicular viewing direction.
Method of providing a security document (1), comprising the steps of:
- providing an image layer (2) with an array of cylindrical lenses (10),
- providing an identification image (4) in an image processing unit (18), the identification image having image elements with predetermined brightness values Bp on a positive brightness scale,
- providing in the image processing unit (18) a positive authentication image (7) corresponding with the first image (4) with picture elements having brightness values that correspond to the brightness values of the identification image (4) and a negative authentication image (8) corresponding with the first image, with picture elements having brightness values Bn that correspond to a reversed brightness scale in which the brightest picture elements in the positive brightness scale appear darkest and the darkest picture elements appear brightest, and laser engraving the first and second authentication images (7,8) through the cylindrical lenses (10) in the image layer (2) at different angles (α1, α2) such that both the identification image (4) and the first authentication image (7) can be observed at a perpendicular viewing direction while the second authentication image (8) can be observed at a non-perpendicular viewing direction.
Dependencies are inferred from the claim text.