1. Introduction
The phenomenon of face spoofing has become increasingly important in biometrics and cybersecurity over the years. Advances in technology, especially in image and video manipulation, have seen the birth of phenomena such as deepfakes, face synthesis, and morphing techniques. The latter consists of gradually transforming a face image into another (Figure 1) and can be used for malicious purposes, for example, to deceive a face recognition system (FRS). In fact, it is possible to obtain false faces containing the characteristics of multiple real faces. The result of this operation can be maliciously exploited to share an identity document [8], as the face resulting from a well-made morphing process can be associated with all the contributing identities by a human operator and an automatic FRS [23]. The problem is even more evident if we consider that such a document can also be used by a terrorist to evade border control.