Abstract: This process for detecting the coming interposition of a mask between an aircraft (A) and a target (C), particularly in a laser-guided weapon firing system, wherein the aircraft has an automatic target tracking system providing an image of the terrain on which the target occupies a permanent fixed position, consists in detecting, during a turn carried out by the aircraft, the points M of this image, marked by their elevation i.sub.m -i.sub.c with respect to the target C, situated in a zone such that i.sub.M -i.sub.C <0 and having an angular progression velocity, with respect to the target, opposite to that of the other points in that zone at the same altitude as the target.Application in particular to laser-guided weapon firing systems.