Yes Limonadinis is right the best practice is always to check with the artist in question simply because they, themselves may not be aware of the license protection. Not everyone reads the fine print.
They may have not custom protected their work and thought it was so they could get angry if you do that with their work or they may be happy to share it.
Either way I think artists are happier if you discuss this with them. You may even make friends or business partners along the way.