This is really impossible to do perfectly. If you want to share something with someone they can take a copy. Unless you are going to go down the DRM route you r

This is really impossible to do perfectly. If you want to share something with someone they can take a copy. Unless you are going to go down the DRM route you really just have to accept that. There are definitely some decentralized system that encourage duplicating data, but even for those that don't you can't escape some users wanting to mirror or archive everything they see.