Face detection and cropping block: this is the first stage of any face recognition system and the key difference between a semi-automatic and a fully automatic face recognizer. In order to make the recognition system fully automatic, the detection and extraction of faces from an image should also be automatic. Face detection also represents a very important step before face recognition, because the accuracy of the recognition process is a direct function of the accuracy of the detection process

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... [Rentzeperis et. al. 2006]. 2. Pre-processing block: the face image can be treated with a series of pre-processing techniques to minimize the effect of factors that can adversely influence the face recognition algorithm. The most critical of these are facial pose and illumination. A discussion on these factors and their significance w.r.t. HMM techniques is given in Section 3. 3. Feature extraction block: in this step the features used in the recognition phase are computed. These features vary depending on the automatic face recognition system used. For example, the first and most simplistic features used in face recognition were the geometrical relations and distances between important points in a face, and the recognition 'algorithm' matched these distances [Chellappa et. al. 1992] ; the most widely used features in face recognition are KL or eigenfaces, and the standard recognition 'algorithm' uses either the Euclidian or Mahalanobis distance [Chellappa et. al. 1992 [Chellappa et. al. , 1995 to match features. Our features and the extraction method used are described in Section 4. 4. Face recognition block: this consists of 2 separate stages: a training process, where the algorithm is fed samples of the subjects to be learned and a distinct model for each subject is determined; and an evaluation process where a model of a newly acquired test subject is compared against all exisiting models in the database and the most closely corresponding model is determined. If these are sufficiently close a recognition event is triggered. Face detection and cropping