There was a one-byte mistake in the distributed Makefile.in for libpng-1.0.61.
At line 610, the version-number should be 2 instead of 3:
I have replaced the libpng-1.0.61.tar.* files at simplesystems and sf.net
If you have already grabbed one of those and built libpng using the
supplied Makefile.in, you'll need to do it over, sorry.
The zip, 7z, and no-config distributions weren't affected and have
not been replaced.
Thanks Paul H. for the report.