Image::PNG::Libpng is a Perl library for accessing the contents of PNG
(Portable Network Graphics) images. Image::PNG::Libpng enables Perl to use
the "libpng" library to read and write files in PNG format.
Image::PNG::Libpng does not contain libpng. It must be installed prior to
installing Image::PNG::Libpng.

Image::PNG::Libpng consists of Perl subroutines which mirror the C
functions in libpng, plus helper subroutines to make it easier to read and
write PNG data in Perl.

For those familiar with libpng, the section the /Differences from libpng
manpage explains the differences with libpng.