1. A method for identifying motor vehicles for monitoring traffic, comprising the following steps: a) recording a perspective image of a motor vehicle under an acute angle with respect to the road, wherein the recorded image contains at least a motor-vehicle view that has a license plate, b) recognizing the license plate in the recorded image and capturing a license-plate contour, c) ascertaining the format of the license-plate contour from the comparison of the corner points of the license-plate contour with stored standardized license-plate formats from a memory, d) ascertaining a calculation rule for perspective rectification of the license-plate contour on the basis of the associated standardized license-plate format, e) producing an image region which is perspectively distorted in a matching manner with respect to the license-plate contour, with a prespecified magnification in dependence on the ascertained format of the license-plate contour, f) extracting the content of the distorted image region surrounding the license-plate contour, and discarding the remaining recorded image of the motor vehicle, g) adapting a license-plate-containing motor-vehicle view, which is extracted from the distorted surrounding image region, to the format of reference images stored in a database, h) rectifying the motor-vehicle view using the calculation rule ascertained from the license-plate contour, i) similarity comparison of the captured contours and their position with those of reference images from the database, and recognizing the greatest correspondence of the captured contours with one of the reference images, and j) categorizing the recorded motor vehicle into a reference-image class, with which the reference image with the greatest correspondence was associated, and outputting a motor-vehicle class derived from the reference-image class.