This is Perl module GD::Chord::Piano.
GD::Chord::Piano installation is straightforward. If your CPAN shell is set up, you should just be able to do
% cpan GD::Chord::Piano
Download it, unpack it, then build it as per the usual:
% perl Makefile.PL % make && make test
Then install it:
% make install
GD::Chord::Piano documentation is available as in POD. So you can do:
% perldoc GD::Chord::Piano
GD:Chord::Piano is hosted on github http://github.com/bayashi/GD-Chord-Piano
This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perlartistic.
Dai Okabayashi <email@example.com>