1. A non-transitory computer-readable storage medium whose contents enable a computing system to detect a building feature in an image having the feature, by performing a method comprising: receiving a target image of a building; computing statistical measures for at least one selected section of the building feature within the target image of the building, the statistical measures determined for each pixel of the image within a sampling window around the pixel; training a statistical model system on the computed statistical measures to identify distinguishing characteristics of the building feature; receiving from the statistical model system indications of portions outside of the selected section of the target image identified as part of the building feature; determining, based on the received indications of portions of the target image, a likely outline of the building feature in the target image; and storing the determined likely outline of the building feature.