11. The computer-implemented method of claim 5 , wherein generating the heatmap of the first image further comprises: determining a respective pixel value for each pixel in the first image based at least in part on a number of visual words in the set of visual words that correspond to a region in the first image that includes the pixel.
12. The computer-implemented method of claim 11 , wherein determining at least one other region in the first image that is connected to the first region further comprises: determining at least one other region in the first image that is adjacent to the first region or overlaps with the first region.