The use of biometric data for user authentication and/or recognition is now a reality. On the other hand, there is still a strong need for new technologies to overpass intrinsic limitations of already "established" techniques. This not only requires to devise new algorithms but to determine the real potential and limitations of existing techniques. This is possible only devising standard testing and assessment procedures based on statistical observations of the outputs of the system. In order to define better standard evaluation process, a system based on space-variant iconic image matching is described and the validation procedure defined. It turns out that all methods based on the same biometric measurements have the same intrinsic limitations, which can be only overcome by the adoption of a multi-modal or multi-algorithmic approach.