1. A computing system for automated generation of descriptors of local regions within a retinal image, the computing system comprising: one or more hardware computer processors; and one or more storage devices configured to store software instructions configured for execution by the one or more hardware computer processors in order to cause the computing system to: access the retinal image; generate a first filtered image using the retinal image, and a morphological filter, computed over a first geometric shape, wherein the first geometric shape is substantially circular or a substantially regular polygon; generate a second filtered image using the retinal image and a morphological filter, computed over a second geometric shape, wherein the second geometric shape has either an elongated or elliptical structure; generate difference image pixel values by computing differences between a plurality of first filtered image pixel values and plurality of second filtered image pixel values; and assign the difference image pixel values as descriptor values, each descriptor value corresponding to a given pixel location of the said retinal image.