“…-Less-constrained recognition could increase the usability and social acceptance of biometric systems [70]. In fact, since they allow a touchless recognition, it would be possible to perform the biometric verification at higher distances, with natural light conditions, and while the traveler is moving, by using the fingerprint [34,35,41,33,30,29,26,39,25,32], the palm [59], or the iris [70,42,27,76,75,37]. A study showed that touchless fingerprint technologies would be preferred over touch-based systems [35], thus allowing for an increased confidence and adoption of biometric recognition [43].…”