A mobile monitoring device including a first sensor for measuring the speed of vehicles passing through a first detection range with a first time stamp; a second sensor for measuring the geometry of vehicles passing through a second detection range with a second time stamp; a camera for recording images of vehicles passing through a third detection range with a third time stamp; and an evaluation device, which calculates from the speed measurement value, first time stamp and first detection range, and from the geometry measurement value, second time stamp and second detection range, the place and time in or at which a passage of the vehicle is to be expected in the third detection range, to determine the matching image on the basis of the third time stamp and third detection range therefrom. The invention additionally relates to such a monitoring method.