1. Method of detecting the presence of a disruptive object on a stretch of road, this method comprising: a) a step of processing images to detect the presence of the disruptive object on the basis of images of the said stretch, b) a step of enumerating the vehicles simultaneously present on the stretch of road on the basis of data gleaned by a first and a second vehicle detector placed respectively at an entrance and at an exit of this stretch, and c) a step of instructing the activation of the image processing step, triggered automatically as a function of the enumeration of step b).