I guess I am not understanding your point of view on textures...
If I take an image of a leaf and use it as a texture for a model, am I licensing the image (which anyone can take) or the artistic view of taking the picture?
OR....
The use of the taken picture in the context of using it as a model texture for a GPL source program?
The declaration of a GPL is indicative that the product (model, texture, et al) is to be used in open source products only without express permission to be used commercially from the original designer and that the code ( for programs ) is freely distributable as long as additions or changes to the code are included with the new incarnation.
Or am I just fishing in the dark?
Regards,
Sean E