A image from the National Geographic is, I think, a different case, because your work would be an image of an image. I would love to use screen grabs from Google Earth, but that is clearly prohibited by the license of the software itself. An image of a mesh is different. It could be argued that a render is not derivative of the mesh (but might be of the texture). Most of the cases that would be likely to really be actionable would be those involving trademark violations, which is a different story. Incidentally, I have contacted some Japanese freestuff providers for permission regarding commercial renders, and the reply I always got was along the lines of my previous post above.