From http://techbase.kde.org/Policies/Licensing_Policy

"Standalone media files such as images may be licensed under the
Creative Commons Attribution-Share Alike 3.0 Unported licence at
http://creativecommons.org/licenses/by-sa/3.0/ . This does not apply
to icons or anything which is likely to be mixed with content under
our normal (GPL etc) licences. "

GPL v2 or later is easiest because that the same licence as most everything else KDE, but CC-BY-SA 3.0 or GPL 3 or later is also possible.

Jonathan
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