Let’s imagine someone once added a file to the IPFS network and published its hash. Currently, the file is no longer available - no node stores it and you cannot retrieve it. If I own a copy of this file, can I prove it by demonstrating that the published IPFS hash corresponds to the file content? How?
If you can re-add the file to IPFS (or just hash it with go-ipfs) and get the original hash, that’s decent proof it’s the same file.
In your hypothetical, even if you don’t know what parameters were used to add the original file it’d be possible to make some educated guesses (e.g. defaults, trickle-dag for video, etc).
Outside of that, I thought I’d read something about trying to store information about how a file in IPFS was originally hashed (maybe in extended attributes) so if someone has the file and adds it back to IPFS it can be added in the same way and produce the same hash.