See: https://bsky.app/profile/alex-gleasonator-dev.eclipse.pub/post/3leciiemkyk2x
Discussion
Do you know how you have to bridge images on Bluesky?
No you cannot simply embed the URL. Bluesky does not support URLs. It only supports an obscure variant of IPFS.
You have to download the entire file, sha256 hash it, get a very specific kind of IPFS CID (but not the normal one), self-host or proxy it, and then embed the CID. I'm kind of amazed my solution works. I basically copied what Ryan Barrett does in BridgyFed.