I am not a lawyer, but the subject of copyright fascinates me.
If you use an R package to create your own code resulting in some original art, I believe you own the copyright to the art and can sell the art. On the other hand if you used someone else's code to recreate their art, then you do not own the copyright to the art.
If you modified someone else's code, then I think it depends on whether you modified it a little or a lot.
Hope that helps.