Susana's interpretation is one clear possiblity, and this is the other, that payable copyright exists and has been paid, and use of the works has been authorised (like "clearing customs" - you declare whatever needs to be paid for, if at all, and having done so, are free to proceed without hindrance.)
The difference is a matter of whether rights for exhibition etc have actually been paid or whether the artists waived their rights. Impossible to tell from the context we have.