Yeah, that's a good point. Kind of ties in with the video I linked. Also reminds me a bit to how in modern video containers the film grain is usually a separate thing, and is rendered onto the image during playback. One can imagine turning on a view where the modified parts of the image would become highlighted, assisting with speculations on what might have been altered and how.
I didn't mention this in my previous comment, but after having thought about it even further, I've eventually arrived at the idea that there can be basically an arbitrary amount of meaning embedded onto a photo or a video, and it being "verified" to me as a human really just means "it is what I think I'm looking at" - that's when I realized this task is likely unsolvable in absolute terms, and just how much more difficulty lies beyond the already hopelessly difficult crackpot idea of light source signal modulation that I came up with prior. But yeah, as I suggested, these are just what I could think of, and perfection should indeed not be the enemy of good.