The image is based on
http://listes.april.org/wws/arc/trad-gnu/2013-09/msg00009/gnu-30-1.fr.svg
by Denis Barbier and Thérèse Godefroy, which is in its turn based on the banner at
http://www.gnu.org/gnu30/
, which is distributed under the Creative Commons Attribution-ShareAlike 2.0 license.

This modified image itself is hence distributed under the Creative
Commons Attribution-ShareAlike 2.0 license as well.