Ultrasound has been trialed in biometric recognition systems for many years, and at present\ndifferent types of ultrasound fingerprint readers are being produced and integrated in portable\ndevices. An important merit of the ultrasound is its ability to image the internal structure of the\nhand, which can guarantee improved recognition rates and resistance to spoofing attacks. In addition,\nambient noise like changes of illumination, humidity, or temperature, as well as oil or ink stains on\nthe skin do not affect the ultrasound image. In this work, a palmprint recognition system based on\nultrasound images is proposed and experimentally validated. The system uses a gel pad to obtain\nacoustic coupling between the ultrasound probe and the userâ??s hand. The collected volumetric image\nis processed to extract 2D palmprints at various under-skin depths. Features are extracted from one of\nthese 2D palmprints using a line-based procedure. Recognition performances of the proposed system\nwere evaluated by performing both verification and identification experiments on a home-made\ndatabase containing 281 samples collected from 32 different volunteers. An equal error rate of 0.38%\nand an identification rate of 100% were achieved. These results are very satisfactory, even if obtained\nwith a relatively small database. A discussion on the causes of bad acquisitions is also presented, and\na possible solution to further optimize the acquisition system is suggested.
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