Re: I've been suspended with a wrong reason...
And for your further education, copyright in inherent -- it exists at the moment a work is created, and it doesn't matter whether the creator of the work is internationally famous or not. It doesn't even matter, in most countries, whether the creator intended to copyright the work, and assignment or revocation (which is impossible in many jurisdictions) of that copyright must be explicit or by statute and pre-existing contract (in the case of "work for hire"). Use of copyright work is only permissible by license, and proof of license is what is required here.
If your artists hold copyright and intend free distribution (so that they can become famous) then they should explicitly license the work under something like the Creative Commons, where licenses for individual works can be registered and verified (at no cost).
“Beware of bugs in the above code; I have only proved it correct, not tried it.” --Donald Knuth
"It was as if its architects were given a perfectly good hammer and gleefully replied, 'neat! With this hammer, we can build a tool that can pound in nails.'" -- Alex Papadimoulis (on TheDailyWTF.com)