1. A method of processing digital vascular images, the method comprising the steps of: providing first and second digital vascular image data; processing the first and second image data with a two-dimensional, directional filter that has the effect of producing clusters of orthogonally adjacent image data points in which the magnitude of an intensity gradient between each orthogonally adjacent image data point is less than a predetermined value; identifying clusters in each of the first and second image data where the magnitude of the intensity gradient between at least one adjacent cluster is greater than a predetermined value; identifying common clusters between the first and second image data where the magnitude of the intensity gradient between at least one adjacent cluster is greater than a predetermined value; and registering the common clusters between the first and second image data.