ed to be the color of the pixel at the top left of
the input image.  If that pixel isn't part of the background, simply
add a one-pixel border at the top of the image, generate the shadow
image, then delete the border from it.

<P>If something goes wrong along the way, the error messages from the
various Netpbm programs <B>ppmshadow</B> calls will, in general,
provide little or no clue as to where <B>ppmshadow</B> went astray.
In this case, Specify the <B>-k</B> option and examine the
intermediate results i