1. An image processing system having at least one processor adapted to control a number of interest points detected in an image frame, the system comprising: an interest point detector configured to identify one or more interest points in a first sub-region of image data associated with an image frame based upon an interest point threshold value; and a rate controller configured to determine the interest point threshold value based at least in part upon a number of interest points identified in a previous sub-region of image data for the image frame.