Abstract: A method of inserting guilloche patterns in a document, each guilloche pattern being capable of encoding variable alphanumeric data ensuring a different aspect at each guilloche pattern so as to render said document secure using an operation of determining an insertion intensity of each guilloche pattern previously generated on the basis of a mid-gray level of the document near said guilloche pattern. A device for implementing this insertion method. The method further provides for extracting guilloche patterns from a secure document likely to be degraded by determining a contrast card of at least one portion of the secure document that includes the guilloche patterns, identifying, on this contrast card an optimal percolation trajectory, and extracting the optimal percolation trajectory, said trajectory corresponding to the guilloche pattern.

Abstract: A method of inserting guilloche patterns in a document, each guilloche pattern being capable of encoding variable alphanumeric data ensuring a different aspect at each guilloche pattern so as to render said document secure using an operation of determining an insertion intensity of each guilloche pattern previously generated on the basis of a mid-gray level of the document near said guilloche pattern. A device for implementing this insertion method. The method further provides for extracting guilloche patterns from a secure document likely to be degraded by determining a contrast card of at least one portion of the secure document that includes the guilloche patterns, identifying, on this contrast card an optimal percolation trajectory, and extracting the optimal percolation trajectory, said trajectory corresponding to the guilloche pattern.