Face recognition [1], the least intrusive biometric technique

in terms of acquisition, has been applied to a wide range

of commercial and law enforcement applications. State-ofthe-

art face recognition systems perform with high accuracy

under controlled environments, but performances drastically

decrease in practical conditions such as video surveillance

of crowded environments or large camera networks. The

main problems are due to changes in facial expressions,

illumination conditions, face pose variations, and presence

of occlusions.