Gartoon Redux is based on Gartoon, which was originally released under GPL v2.
Later the author re-released Gartoon under GPL v2 or later. Relevant e-mail
(with headers trimmed):

Message-Id: <C3FBD5B1-4400-4AFE-84B4-688E6442EBB8@gmail.com>
From: Kuswanto <zeussama@gmail.com>
To: =?UTF-8?Q?Krzysztof_Kosi=C5=84ski?= <tweenk.pl@gmail.com>
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Subject: Gartoon GPL v2
Date: Wed, 7 Jan 2009 08:26:56 +0700
X-Mailer: Apple Mail (2.930.3)

I release Gartoon icons under GPL v2 or, at the licensee's option, any  
later version

Copyright:

Gartoon Redux is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; either version 2, or (at your option) any later version.

Gartoon Redux is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.  See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with
Gartoon Redux; see the file COPYING.  If not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.

On Debian systems, a copy of the GNU General Public License is available in
/usr/share/common-licenses/GPL as part of the base-files package.
