1. Method of watermarking a color image that has at least three components, wherein the method comprises: a computer performing: an insertion step of a mark of watermarking, on at least one point of the image, according to an insertion rule taking into account the relative position of three component vectors associated to said at least one point, wherein, for each of said related points, the method comprises: a step of calculating the distance between any two vectors of said at least three vectors, a step of selecting two vectors as reference vectors and one vector to be marked in order to bear said mark of watermarking, said reference vectors being those the furthest away from each other, and said vector to be marked is a central vector, positioned between said reference vectors.