1. An image processing method for a driver assistance system of a motor vehicle for detecting and classifying at least one portion of a predefined image element having a road sign in a selected digital image captured by an image sensor of the driver assistance system, comprising: computing first scale-invariant image features and relative geometric arrangement of the first scale-invariant image features with respect to one another based on at least one image region of the digital image; comparing, by a classifier unit of the driver assistance system, the first scale-invariant image features and the relative geometric arrangement of the first scale-invariant image features with respect to one another to second scale-invariant image features and relative geometric arrangement of the second scale-invariant image features with respect to one another which are computed based on the predefined image element; and determining, by the classifier unit, the at least one portion of the predefined image element of the digital image to be detected and classified if the comparing produces a match, wherein a measure for the correctness of the detection and classification is determined, and wherein a number of pixels of the second scale-invariant image features associated with pixels of the first scale invariant image features is used as the measure for the correctness of the detection and classification.