If you are missing file chunks, you specify the leaf numbers you are missing. Each leaf is labeled with a number. Total number of leaves are within the merkle root block.
No, you can request a photo with its merkle root on nostr:npub1h0rnetjp2qka44ayzyjcdh90gs3gzrtq4f94033heng6w34s0pzq2yfv0g just like you can request a photo with its hash on blossom.
Discussion
This^ missing file chunk retrieval process is performed automatically — users don’t need to think about it. Was just describing how it works under-the-hood.
I don’t think supporting a whole file hash is a good idea. Files should be chunked. We’re not going to support both ways. It’ll be backwards compatible with the original method of centralized website, and with merkle roots. Blossom is the wrong path.