The error and variance is very dependent on outliers,
which usually occurs when the images contains shadows or
the texture is poor. In these situations the similarity image
contains several peaks, where the highest ones are candidates
to be the selected match. Shadows can be reduced and texture
can be enhanced by improving the illumination. The system
is also sensitive to missing frames. However, these are both
easy to detect and to compensate for, for instants by double
the search area in next image.