In principle, high-precision imaging of human vascular structures, including thoseinside the human hand, is a solved problem. Figure1.1a displays correspondingvessels using a Magnetic Resonance Angiography (MRA) medical imaging device,while Fig.1.1b shows the result of applying hyperspectral imaging using a STEM-MER IMAGING device using their Perception Studio software to visualise the datacaptured in the range 900–1700nm. However, biometric sensors have a limitation interms of their costs. For practical deployment in real-world authentication solutions,the technologies used to produce the images in Fig.1.1 are not an option for this rea-son. The solution is much simpler and thus more cost-effective Near-Infrared (NIR)imaging.Joe Rice (the author of the Foreword of this Handbook) patented his NIR-imaging-based “Veincheck” system in the early 1980s which is often seen as the birth ofhand-based vascular biometrics. After the expiry of that patent, Hitachi, Fujitsu and Tech sphere launched security products relying on vein biometrics (allholdingvariouspatents in this area now). Joe Rice is still involved in this business, as he is partneringwith the Swiss company BiowatchID producing wrist vein-based mobile recognition technology. The physiological background of this imaging technique is as follows. Thehaemoglobin in the bloodstream absorbs NIR light. The haemoglobin is the pig-ment in the blood which is primarily composed of iron, which carries the oxygen.Haemoglobin is known to absorb NIR light. This is why vessels appear as darkstructures under NIR illumination, while the surrounding tissue has a much lowerlight absorption coefficient in that spectrum and thus appears bright. The blood inveins obviously contains a higher amount of deoxygenated haemoglobin as com-pared to blood in arteries. Oxygenated and deoxygenated haemoglobin absorb NIRlightequallyat800nm,whereasat760nmabsorptionisprimarilyfromdeoxygenatedhaemoglobin while above 800nm oxygenated haemoglobin exhibits stronger absorp-tion [68, 161]. Thus, the vascular pattern inside the hand can be rendered visible withthe help of an NIR light source in combination with an NIR-sensitive image sensor.Depending on the used wavelength of illumination, either both or only a single typeof vessels is captured predominantly.