1. A method for processing a sequence of input images securely, comprising: acquiring, in a client, a sequence of input images, each input image including pixels; permuting randomly, in the client, the pixels in each input image according to a permutation π to generate a permuted image for each input image; transferring each permuted image to a server; maintaining, in the server, a background image from the permuted images; combining, in the server, each permuted image with the background image to generate a corresponding permuted motion image for each permuted image; transferring each permuted motion image to the client; and reordering, in the client, the pixels in each permuted motion image according to an inverse permutation π −1 to recover a corresponding motion image for each input image.