1. A method for estimating a velocity field using an image sequence having more than two frames, the method comprising: providing a set of equations including an integer number M−1 displaced frame difference equations, where M is greater than 2; receiving an input image sequence comprising at least M image frames individually including multidimensional image data corresponding to a plurality of pixel locations at M different times; and using at least one processor, solving the equation set using a set of iteration equations and the image data of the M image frames to determine a velocity field describing velocity vectors at pixel locations at a first one of the M different times.