Free media license
A free media license allows distribution (including commercial use) and manipulation of media. Releasing derivate works under the same license (copyleft) and attribution to the original author(s) can be enforced by such a license.
Free media can also be licensed under one of the free source code licenses. However, there is less legal clarity in the use of source code licenses for media. On the other hand, the strong copyleftness of, for example, the GPL, makes such licensing convenient and, by some interpretations, even necessary.