I. Introduction
Face recognition is a popular method for authenticating and identifying users, such as for access to secure facilities or devices, for law enforcement purposes, or to locate missing persons. A closely related technology is face verification, which is the process of verifying that a person is who they claim to be. It is a one-to-one matching problem, where the system is trying to match the face in the image to a specific person's identity. Face recognition or verification relies on image processing to extract features from faces. These features are then used as input to pattern recognition methods that can identify and match faces. Increasingly, these pattern recognition methods are based on machine learning, such as deep learning networks. Deep learning has been shown to be effective in extracting information from facial images. Trained on large data sets of facial images, deep learning models can learn to identify and extract a wide variety of features from faces, such as the shape of the face, the eyes, the nose, the mouth, and the eyebrows.