version: 1.2.32
source: libpng.org

This is a part of my UnixImageIO framework. A script is available to build the framework from sources.

Important note: Security holes in earlier versions of libpng are fixed quickly when found. Please make sure to get the latest version of the source.

change the lines:

typedef unsigned long png_uint_32;
typedef long png_int_32;

to:

typedef unsigned int png_uint_32;
typedef int png_int_32;

In the libpng source:

export MACOSX_DEPLOYMENT_TARGET=10.5
./configure --disable-static --without-libpng-compat --disable-dependency-tracking \
CFLAGS="-Os -arch ppc -arch i386 -arch ppc64 -arch x86_64"
make
sudo make install

No need for pngconf.h patch.

In the libpng source:

export MACOSX_DEPLOYMENT_TARGET=10.4
./configure --disable-static --without-libpng-compat --disable-dependency-tracking 
CFLAGS="-Os -arch ppc -arch i386 -isysroot /Developer/SDKs/MacOSX10.4u.sdk"
make
sudo make install

On Panther and for a generic single-arch build.

In the libpng source:

./configure --disable-static --without-libpng-compat --disable-dependency-tracking CFLAGS=-Os
make
sudo make install