  To date, most facial expression analysis have been based on posed image
databases and is carried out without being able to protect the identity of the
subjects whose expressions are being recognised. In this paper, we propose and
implement a system for classifying facial expressions of images in the
encrypted domain based on a Paillier cryptosystem implementation of Fisher
Linear Discriminant Analysis and k-nearest neighbour (FLDA + kNN). We present
results of experiments carried out on a recently developed natural visible and
infrared facial expression (NVIE) database of spontaneous images. To the best
of our knowledge, this is the first system that will allow the recog-nition of
encrypted spontaneous facial expressions by a remote server on behalf of a
client.
