e of the same dimensions as T, with
 each entry being 0 or 1, where zero specifies regions to ignore (the
 ground) and 1 specifies interesting regions (the figure).  Essentially Tm
 specifies regions in T that are interesting and should be taken into
 account when doing normalized cross correlation. This allows for
 templates of arbitrary shape, and not just squares. Note: with a mask,
 this function is approximately 3 times slower because it cannot use the
 trick of precomputing running sums.

 USAGE
  C =