1. A method of matching background regions between a reference image and a target image, comprising (a) determining the background regions for the reference image and the target image; (b) locating feature points in the background of the reference and target images; (c) matching feature points in the reference and target images; (d) clustering matched points in the target image into spatially compact regions in an image coordinate space to produce a set of target clusters; (e) clustering matched points in the reference image into spatially compact regions in the image coordinate space to produce a set of reference clusters; (f) finding a matching target cluster for each of the reference clusters by counting a number of matched points between target and reference clusters; (g) removing reference clusters based on the count of the number of matched points; (h) computing a match score between the reference and target images from the remaining reference clusters; and (i) using the match score to determine whether the reference and target images are captured in the same location.