Licensing of wallpapers

Hello everybody,

in the Visual Design Group forum there's currently a wallpaper 
discussion going on. The question arose of how these wallpapers may be 
licensed to be able to be shipped alongside Plasma Next. [1]
Some users are wondering if wallpapers have to be GPL3 only or if a CC 
license is also acceptable and if yes, then which CC license comes into 
question.

Thank you in advance

Phil

[1] http://forum.kde.org/viewtopic.php?f=285&t=120497