Biometric recognition systems based on 3D information of palmprint have been experimented with in the last years. Optical technology is the most widely used, but it provides information on the external surface only. Ultrasound, instead, allows obtaining information that accounts for principal lines depth. In this work, a 3D palmprint recognition system, based on images acquired through an Ultrasound system by using water or gel as a coupling medium between the probe and hand, is proposed and tested. In both cases, a 3D template that contains information on the depth of principal lines is generated by combining 2D templates obtained from images extracted at various under-skin depths. The performances of the system have been evaluated through...