1. A method of analysis, comprising: registering a target image to define a plurality of keypoints arranged in sets corresponding to polygons or linear segments in the target image, said registering comprising ordering keypoints of at least one set, according to descriptor vectors associated with said keypoints in said at least one set, so as to reduce an overall number of said sets, said ordering being by an ordering operator calculated by applying to said database a procedure for detecting keypoints together with associated information to provide a group of features, and projecting said descriptor vectors onto a first principal component of said group of features; accessing a database of registered and annotated images, and employing a polygon-wise comparison between the target image and each database image; and using said comparison for projecting annotated locations from said database images into the target image.