As long as you know how to edit metadata, you can definitely fool minor “trust systems” like adjusters, police, etc. It’s a big gap. (For any future readers, no I have not done this and would never do it, really.)
The only solution I see is some kind of hardware-linked signature showing that the image was produced at a certain time, by a certain device. In theory, you could make this signature somewhat “provable” and anchored to a specific time by combining something like 1) the latest Bitcoin block hash, and 2) a blockchain anchor, thereby proving that the photo was taken within a certain time widow after the hash was known and before the anchor was published. But even that arrangement is highly susceptible to hardware attacks.
A service will allow you upload a file and attach a date and signature. Additionally, you add the email addresses of anyone else that needs to also date and sign. The service then verifies all signatures and then dates and signs. Then it makes a SHA-512 hash, publishes it next to the signatures on its site and then publishes a url including the hash on the blockchain. When someone visits that link, they can see the hash of the file, dates, signatures and a final hash of everything. Anyone wishing to view the actual file must be able to prove their identity using their private key (or alternatively, host an encrypted version for each signer). Thus anyone can prove a few things:
1. You agreed that the document was correct on the date you signed. You can't date your signature any earlier than when the file was uploaded. This prevents you from uploading the wrong version of a document or predating your signature well in the past. It's like signing in front of a notary.
2. The additional person can verify the document is correct (no contract clauses have been edited, a photo is legit, etc). This gives credence to what you've posted, especially important for a contract.
3. The service verifies that the file you uploaded matches what everyone signed and the date everyone supplied is in the past. A requirement could be that everyone involved needs to have their public keys published on a well-known key server that at least verifies email addresses. A better option would be one that verifies through physical identity documents. Even better would be if your national ID card had PKI keys. Regardless, the service ensures that each signature has been tied to some sort of identity and that the signatures are all valid.
4. The hash published on the blockchain again can confirm that at the time of publishing, everyone agreed to the contents of the file and that everyone signed when they did. If someone claims the file was changed, we can simply verify the signatures and as long as no one was impersonated, we can prove that signers A, B, and C all signed a copy of the same document on dates X, Y, and Z.
5. The original document is still available for signer that still has their private key, even if it's expired. Additionally, the service has their own copy of the file that can be subpoenaed if necessary.
The entire system ensures a file has not been changed in any way since it was first published (via the signatures), real people have arrested to its truth (via public key verification), and that the attestation has not changed (via publishing the hash of all signatures on the blockchain). Additionally, nothing can be deleted without signed deletion requests from all signers.
You could potentially do this without the neutral 3rd party but then there's no verification when you actually attested to its truth, only that you published that attestation on the blockchain publication date.
The only solution I see is some kind of hardware-linked signature showing that the image was produced at a certain time, by a certain device. In theory, you could make this signature somewhat “provable” and anchored to a specific time by combining something like 1) the latest Bitcoin block hash, and 2) a blockchain anchor, thereby proving that the photo was taken within a certain time widow after the hash was known and before the anchor was published. But even that arrangement is highly susceptible to hardware attacks.