You can that sort of do with nostr too by embedding an url to an image. Later on you can change that image. To prevent that, nostr should add something like etags (sha256 checksum) to an event for links to static elements. Clients can then check their validity. Also relays could prefetch these static files and provide them to clients in additional http requests. Clients can verify them by the etags. This would make nostr safer and easier to scale,.since static content is distributed.