Human beings have always used two main modes to communicate verbal and non-verbal ways that use words and facial expressions respectively. The human face provides a rich source of information and is associated with the signalling of emotions and pain (Ekman, 1993), the personality traits, the communicating of emphatic understanding (Bavelas et al., 1986) and the regulation of conversations (Cohn and Elmore, 1988). Furthermore, emotions are fundamental to human lives and decision-making. Therefore, variation of the human face has been a subject of interest since ancient times, and in recent years, we have witnessed the rapid emergence of an interest for the automated analysis and interpretation of facial activity through computer vision.