Easiest thing to do is to create a hash and store the hash on the blockchain. Similar to how Simple Proof has used Open Timestamps to ensure election documents weren't tampered with by putting a hash of the documents onto the blockchain. This proves the document's existence and content at a certain point in time. If that document is presented with different content, even by a single byte, at a later time, the hash won't match. Proving that it was altered.
Discussion
I think it’s only Bitcoin that has the immutable blockchain?
Correct. But a hash of the data is a far more responsible use of the block space than putting the entire file on the blockchain. Then the file can be saved anywhere and anyone can verify its contents by comparing a hash of the file against the record of that hash on the blockchain to verify it hasn't changed.
👍 makes sense. So as the community is taking sides re: filtering, seems that financial hashes, nice and small, if passing a filter add value to BTC. So there is some middle ground.
There's not really any such thing as a "financial hash." You can't tell from looking at a hash what type of data was used to create the hash, financial or otherwise. Only by having access to the original data and running the hashing algorithm can you tell that the hash came from that data. Yet, it proves that the data existed in that form at that time. If the data included ownership information, then the hash also proves ownership at that time.