Palmprint: The inner part of the hand is called palm and the extracted region of interest in between fingers and wrist is termed as palmprint as shown in Fig. 1(a). Pattern formation within this region are suppose to be stable as well as unique. Even monozygotic twins are found to have different palmprint patterns [16]. Hence one can consider it as a well-defined and discriminative biometrics trait. Palmprint׳s prime advantages over fingerprint includes its higher social acceptance because it is never being associated with criminals and larger ROI area as compared to fingerprint. Larger ROI ensures abundance of structural features including principle lines, wrinkles, creases and texture pattern (as it is evident in Fig. 1(a)) even in low resolution palmprint images. This enhances system׳s speed, accuracy and reduces the cost. Some other factors favoring palmprint are lesser user cooperation, non-intrusive and cheaper acquisition sensors.
Knuckleprint: The horizontal and the vertical pattern formation in finger knuckleprint images (as shown in Fig. 1(b)) are believed to be very discriminative [47]. The knuckleprint texture is developed very early and lasts very long primarily because they are on the outer side of the hand, hence safely preserved. Its failure to enroll rate (FTE) is observed to be lower as compared to fingerprint and can be acquired easily using an inexpensive setup with lesser user cooperation. The user acceptance favors knuckleprint as unlike fingerprint they are never being associated to any criminal investigations. A comparative study between palmprint and knuckleprint based over the biometric properties is presented in Table 1.