*3.4.1.1. Palm vein authentication systems*

The heat pattern of the human body may easily be determined by IRT. The heat pattern of veins in the human hand is specific to each individual. Thus, the structure of the hand veins may be determined, and private ciphers may be created [28, 29]. Sarkar et al reported that "the red blood cells (hemoglobin) present in the veins absorb the rays and show up on the map as black lines, whereas the remaining hand structure shows up as white" [29]. Some companies have begun to use palm vein authentication systems in automatic teller machines (ATMs) worldwide. These systems have also been used in the entrance into a country from the airport, as well as the entrances of several security buildings.

## *3.4.1.2. Facial recognition systems*

Facial recognition systems consist of three modules, including image acquisition, face recog‐ nition and face matching. In this system, visible light, IR light and thermal cameras are used to obtain a three-dimensional image and improve the image resolution [29].

## *3.4.1.3. Iris scanning systems*

The iris is in a position to be seen at first glance and is easily defined in the IR cameras and visible-light cameras. Therefore, the iris may be easily used in automatic recognition systems. In this system, cooperation in the placement of the eye in the correct place of the device is sufficient [27–29].
