AverageImages - part of ANTS registration suite
       Usage:
       ./AverageImages ImageDimension Outputfname.nii.gz Normalize <images>
              Compulsory arguments:
              ImageDimension: 2 or 3 (for 2 or 3 dimensional input).
              Outputfname.nii.gz: the name of the resulting image.
              Normalize:  0  (false)  or  1  (true); if true, the 2nd image is
              divided by its mean. This  will  select  the  largest  image  to
              average into.
              Example Usage:
       ./AverageImages 3 average.nii.gz  1  *.nii.gz