The disclosed method and system may be used for creating advanced protection means for secure items (e.g. bank notes, identity documents, certificates, checks, diploma, travel documents, tickets) and valuable products (e.g CD-ROMs, DVD's, prescription drugs, products with affixed labels, watches). 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. By modifying the relative superposition phase of the revealing layer on top of the base layer or vice-versa (e.g. by translation or rotation), shape level lines grow and shrink dynamically. In the case that these shape level lines are present, the secure item is accepted as authentic. Otherwise the item is rejected as suspect.