1. A method comprising: receiving a sequence of images and selecting one of the images as a reference frame image; determining whether an N-th frame image has acute movements relative to the reference frame image according to a predetermined threshold; and if there are acute movements, compressing and transmitting the N-th frame image; if there are no acute movements, neither compressing nor transmitting the N-th frame image; increasing N by 1 and repeating above operations till the sequence of images is over.