A method of inserting additional information, such as a digital signature, in a digital image comprises the following steps: detecting (E10) the points of interest in said image (I); selecting (E11) a subset of points of interest adapted to define a geometric reference frame in said image (I); calculating (E12), for the geometric reference frame, reference information necessary for determining the geometric transformation applied to the image for a class of predetermined geometric transformations; coding (E13) said reference information in a reference key (Kr); and inserting (E16-E19) the additional information in said digital image (I). Use notably for geometrically re-fixing the image before extracting the signature.