If you post it you can copy paste the link of the pic.

No media is (typically) hosted by relays, although there's a NIP for that (95)

Clients like amethyst have several options integrated that you can pick from to upload image/media, so from a UX standpoint it works just like any other app where you upload to a central server.

Because Damus is weird. Will just needs to implement this change. Amethyst allows you to upload banners.