Who posts raw output from cameras anywhere? This doesn't seem useful outside some niche use-cases (like security camera footage). At a minimum just about every recording is going to be re-compressed for streaming.
I'm not aware of any secure digital signature schemes that don't require the thing they signed to be bit-for-bit identical to pass verification. There are perceptual hashing algorithms that could theoretically be used to build such a scheme, but such hashes are not second preimage resistant, so someone could create a modified video that still passes signature verification.
I suppose the validator could do a fuzzy match and just output a similarity score that compares the result to the original image. IE - This image is 75% similar to the original with something like a perceptual hash. Then it's the users problem to decide if 75% is close enough for their trust.
You want it visually identical but not necessarily bit-for-bit identical. Compression and transcoding should not cause validation to fail unless the compression artifacts are particularly severe, but even a tiny, one-pixel change that substantially alters the appearance of the photo should cause validation to fail.
And yes I agree this is hard to quantify and impossible with existing algorithms, that was my point.
You'd also need close to 100% adoption for this to be effective, otherwise people will just assume the fakes were recorded with one of the cameras that doesn't have that feature, or that they didn't bother to upload the raw footage anywhere.