In this paper we present a new approach to classifying radiographs, which is the first important task of the IRMA system. Given an image, we compute posterior probabilities for each image class, as this information is needed for further IRMA processing. Classification is done by using an extended version of Simard's tangent distance within a kernel density based classifier. We propose a new distortion model for radiographs and prove its effectiveness by applying the method to 1617 radiographs coming from daily routine. Although the distortion model alone yields very good results, the best recognition rates are obtained by combining it with tangent distance, i.e. by computing a `distorted tangent distance'.