Patent ID: 8885947

Claim:
A method for marking graphical elements comprising the steps of: estimating axes of alignment of characters and symbols in said graphical element; defining zones of high visibility around these axes of alignment; defining at least one zone of low visibility comprising parts of said graphical element that are not comprised in any of said zones of high visibility; selecting at least three coherent edge portions of said graphical element in said at least one zone of low visibility, such that the relative orientation of said coherent edge portions is constant or smoothly varies along their entire length, said at least three coherent edge portions comprising at least two reference edge portions and one edge portion to mark located between said at least two reference edge portions; defining a family of smooth and non-intersecting curves, said curves intersecting all of said at least three coherent edge portions; defining an encoding area comprising said at least three coherent edge portions and said curves, said encoding area being limited on two opposite sides by said at least two reference edges portions and on two other opposite sides by curves of said family of curves; shifting said edge portion to mark along said curves relative to said at least two reference edge portions; and storing information about said at least one encoding area in a descriptor of said graphical element.