You just need to the broadcast notes to them
Okay so if I understand correctly, I should set up my own relay with my users' notes. Those notes contain the image URLs only (actual image data will be stored by me), and then my relay should broadcast these notes to other relays, who will automatically pick them up?
If you’re going to store the media, I suggest reading nip-96 or check out Blossom. https://github.com/nostr-protocol/nips/blob/master/96.md https://github.com/hzrd149/blossom