Which type of scan is used on the eye to measure the layer of blood vessels?

Facial recognition analyzes the geometric structure and features of the face, such as the distance between eyes and nose shape, not eye blood vessels.

The retina is a thin layer of tissue at the back of the eye containing a highly unique network of blood vessels that differs between individuals and even between a person's two eyes. A retinal scan illuminates these vessels with low-intensity infrared light and captures their pattern for authentication. This is distinct from an iris scan, which captures the textured pattern of the iris - the colored ring visible at the front of the eye.

An iris scan analyzes the unique texture and patterns of the iris - the colored portion at the front of the eye - not the blood vessel layer behind it.

Signature kinetics (dynamic signature verification) measures behavioral characteristics such as pen pressure and speed during signing, not any eye-related feature.