Why not define a blossom://
Latest PR for #blossom
https://github.com/hzrd149/blossom/pull/13
This defines the the k:10063 event and how clients can use it to repair broken URLs
If your a nostr client dev id like to get your feedback on this one, since its something that needs to be implemented on the client side
Discussion
That would work just as well for blossom, but using the servers domain + sha256 as a URL allows it to be backwards compatible with any web browser or client that renders images from URLs
Makes sense. That is how I've already implemented the blossom integration in my app (just with a different 'kind' for server list - I'll switch it to standard)
Oh wait I've already used the right kind... has this bud been around longer? Somehow I've already implemented this exact flow in my app