1. A method for determining optical flow of a region of interest, the method comprising the steps of: capturing with an imager a plurality of images of one or more objects on a moveable structure, the plurality of images comprising a first image and a second image; partitioning the second image into a plurality of data blocks; comparing a set of one or more of said blocks with at least a portion of the first image: determining the displacement between the first image and block for each of the blocks in which a match is detected; identifying the non-zero displacement common to the most blocks; and associating the most common displacement with the moveable structure and one or more objects.