The *.png and README.original files in this directory are copied from
libpng.org, specifically contrib/pngsuite/* in libpng-1.2.40.tar.gz.
README.original gives the following license for those files:

	Permission to use, copy, and distribute these images for any purpose
	and without fee is hereby granted.

The *.sng files in this directory were generated from the *.png files
by the sng command-line tool.