1. A computer-implemented method of processing a fingerprint image, comprising: acquiring a present fingerprint image from a fingerprint sensor and computing a plurality of first feature vectors of the present fingerprint image; retrieving a plurality of second feature vectors of an enrolled fingerprint image from a storage; applying a similarity measure to compute a plurality of similarity values that represents a degree of similarity between a set of first feature vectors and second feature vectors; performing first classification of at least a portion of the plurality of similarity values to generate a first signal indicative of whether the present fingerprint image falls within a class defined from enrolled images; performing second classification of at least a portion of the plurality of similarity values to generate a second signal indicative of whether the present fingerprint image falls within a class of fingerprints from live fingers or a class of fingerprints from imitated fingers; generating an authentication signal from the first signal and the second signal; characterized in: matching first feature vectors and second feature vectors to form a first set of matching pairs; reducing the first set of matching pairs to a second set of matching pairs that comprises those matching pairs that agree to a uniform geometrical transformation; wherein computation of the plurality of values of the similarity measure is restrained to be computed from the pairs of first feature vectors and second feature vectors that falls into the second set of matching pairs; wherein the first feature vectors and the second feature vectors that fall outside one or both of the first set of matching pairs and the second set of matching pairs are collected in a first set of outlier features; and wherein one or both of the first classification and the second classification includes all or at least a portion of the outlier features in generating the first signal and the second signal, respectively.