Shear a PNM image. More information: https://netpbm.sourceforge.net/doc/pnmshear.html.
pnmshear angle path/to/input.pnm > path/to/output.pnm
pnmshear -background blue angle path/to/input.pnm > path/to/output.pnm
pnmshear -noantialias angle path/to/input.pnm > path/to/output.pnm