This book discusses human–computer interaction (HCI) which is a multidisciplinary field of study which aims at developing and implementing  tools and techniques to attain an effective and efficient interaction between the humans (the users) and computers. In recent years, there is an increase of interest of HCI researchers and practitioners in the inclusion of gaze gestures which can greatly enhance the communication between the human user and the computer, as well as other more “physical” communication involving all what can be learned from movements of the human body, from face,...