If you want to develop programs which will manipulate PNG image format
files, you should install libpng.
drwxr-xr-x 2 root root 0 Jan 4 2004 /usr/doc/libpng-1.2.5 -rw-r--r-- 1 root root 68289 Oct 3 2002 /usr/doc/libpng-1.2.5/CHANGES -rw-r--r-- 1 root root 14340 Oct 3 2002 /usr/doc/libpng-1.2.5/README -rw-r--r-- 1 root root 1182 Dec 23 2000 /usr/doc/libpng-1.2.5/TODO -rw-r--r-- 1 root root 29664 Oct 3 2002 /usr/doc/libpng-1.2.5/example.c -rw-r--r-- 1 root root 125220 Oct 3 2002 /usr/doc/libpng-1.2.5/libpng.txt -rw-r--r-- 1 root root 136663 Jan 4 2004 /usr/include/png.h -rw-r--r-- 1 root root 40750 Jan 4 2004 /usr/include/pngconf.h -rw-rw-rw- 1 root root 139002 Jan 4 2004 /usr/lib/libpng.a -rw-r--r-- 1 root root 45489 Jan 4 2004 /usr/share/man/man3/libpng.3.gz -rw-r--r-- 1 root root 2252 Jan 4 2004 /usr/share/man/man3/libpngpf.3.gz -rw-r--r-- 1 root root 954 Jan 4 2004 /usr/share/man/man5/png.5.gz