ragnarok2040 has updated the libpng library port to PS2.

Release notes:

I’ve updated the libpng port to 1.2.33. I uploaded a tarball of the source and a patch to update the current port to 1.2.33 to http://homebrew.thewaffleiron.net/ragnarok2040. The tests in pngtest.c passed and gsKit’s png-texture example worked fine. You should make sure previous header and library versions of libpng aren’t installed otherwise it might get linked in when building pngtest.c.

http://forums.ps2dev.org/viewtopic.php?t=11254