facilitate the user s task. One such approach is the

object-related image retrieval. In the context of face

images, it is of interest to retrieve images based on

people s names and facial expressions. However, when

images of the database are allowed to appear at dif-

ferent facial expressions, the face recognition approach

encounters the expression-invariant problem, i.e. how

to robustly identify a person s face for which its learn-