The invention includes processing an image belonging to a sequence of at least two images displaying a surface representing an organ or part of an organ which is deformable over time and called the organ surface. The organ surface includes characteristic points (marking points) which correspond to each other from one image to another in the sequence. The method includes defining a structure per unit length whose deformation is followed on an image, calculating the positions of the marking points and determining the parameters of a mathematical expression of the deformation of the organ observed between the two images. The determination is carried out from positions of a set of marking points on the two images. The expression is applied to the structure per unit length to define the form of the structure per unit length after deformation of the organ between the two images.