Allow to upload artwork, tag another artist (comission or grupal art) and if him/her agrees, the artwork will be shown as if uploaded by the artist, but the faves and comments will be shared.
I have the same problem.
Customer support service by UserEcho
Almost any browser has that little thing called "save picture as" which cannot be disabled. reliably. Even if you put something invisible above like some websites does to prevent from it, you can always rely on good ol' F12 on Firefox, Chrome, Edge and even Internet Explorer. If you don't want people to download your artwork, don't upload it. If you don't want people to get the full res images for free just upload lower res ones.