And of course it will be impossible to remove this watermark programs can see programmatically because humans can't see it, right?
I mean, go for it if you want. We're already, today, past the point where a photo or video in and of itself constitutes reliable evidence due to how close known tools can get. You need to show chain of custody like you would any other forensic evidence, including a credible original source on the record, for it to be actually reliable. Faking anything is absolutely plausible.