A method for generating a density image of an observation zone over a given time interval, in which method a plurality of images of the observation zone is acquired, for each image acquired the following steps are carried out: a) detection of zones of pixels standing out from the fixed background of the image, b) detection of individuals, c) for each individual detected, determination of the elementary surface areas occupied by this individual, and d) incrementation of a level of intensity of the elementary surface areas thus determined in the density image.