1. A method for classifying a banknote or a coin, the method comprising: performing a plurality of measurements on a test specimen; deriving a plurality of K-dimensional local feature vectors each having K components and each based on a respective group of said measurements; combining each of the K components of each local feature vector with the corresponding components of the other local feature vectors in a data reduction operation to obtain a global feature vector; calculating a distance between the global feature vector and a vector represented by stored data associated with a target denomination; and indicating, in dependence on the calculated distance, whether or not the test specimen is genuine currency of said target denomination.