pnmmargin
Add a border to a PNM image.
TLDR
Add a border of the specified size to a PNM image
$ pnmmargin [size] [path/to/image.pnm] > [path/to/output.pnm]
Specify the color of the border
$ pnmmargin -color [color] [size] [path/to/image.pnm] > [path/to/output.pnm]
