1. A computer-implemented method, implemented by hardware in combination with software, the method comprising: for each particular template image of a plurality of template images: (A) determining a first set of feature points associated with said particular template image; (B) determining a second set of feature points associated with said particular template image, said second set of feature points (i) being a subset of said first set of feature points, and (ii) comprising fewer feature points than said first set of feature points; (C) associating said first set of feature points and said second set of feature points with said particular template image.