1. A computer-implemented method for discriminating coins, the method comprising: acquiring a sensor signal of a coin; generating a fingerprint having a plurality of sampled sensor points from the sensor signal; calculating an appraisal from the fingerprint and a linear discriminant vector, wherein the linear discriminant vector is an inverse of a covariance matrix, and wherein the covariance matrix includes a valued training matrix from a valued coin population and an impostor training matrix from an impostor coin population; and comparing the appraisal to a threshold to discriminate the coin.