A starting contour is defined surrounding around an elementary object delimited by a natural contour in a video image. On the basis of the starting contour, an original active contour is defined, formed by a set of nodes distributed on this starting contour, each node being formed by a point belonging to this starting contour and by an elastic energy function representative of the distance separating this node from a neighbouring node. With regards to a set of reference values representative of the contour of this object, the active contour is subjected to a convergent deformation under a blocking condition, by displacing at least one of the nodes of the original active contour toward the natural contour of the elementary object to generate a current active contour iteratively subjected to this convergent deformation.