Authentication of secure items by shape level lines
The disclosed method and system may be used for creating advanced protection means for various categories of documents (e.g. bank notes, identity documents, certificates, checks, diploma, travel documents, tickets) and valuable products (e.g. optical disks, CDs, DVDs, CD-ROMs, prescription drugs, products with affixed labels, watches) hereinafter called "secure items". Secure items are authenticated by shape level lines. The shape level lines become apparent when superposing a base layer comprising sets of lines and a revealing layer comprising a line grating. One of the two layers is a modified layer which embeds a shape elevation profile generated from an initial, preferably bilevel, motif shape image (e.g. typographic characters, words of text, symbols, logo, ornament). In the case of an authentic document, the outline of the revealed shape level lines are visual offset lines of the boundaries of the initial bilevel motif shape image. In addition, the intensities, respectively colors of the revealed shape level lines are the same as the intensities, respectively colors of the lines forming the base layer sets of lines. By modifying the relative superposition phase of the revealing layer on top of the base layer or vice-versa (e.g. by a translation or a rotation), one may observe shape level lines moving dynamically between the initial bilevel motif shape boundaries and shape foreground centers, respectively background centers, thereby growing and shrinking. In the case that these characteristic features are present, the secure item is accepted as authentic. Otherwise the item is rejected as suspect. Pairs of base and revealing layers may be individualized by applying to both the base and the revealing layer a geometric transformation. Thanks to the availability of a large number of geometric transformations and transformation parameters, one may create documents having their own individualized document protection. The invention also proposes a computing and delivery system operable for delivering base and revealing layers according to security document or valuable product information content. The system may automatically generate upon request an individually protected secure item and its corresponding authentication means.