I've done probably a few hundred northerns in the 24 years I've been doing taxidermy and this fish looks pefectly legit to me. Not saying it is, as I have no way to verify it, but as far as the photo, color, and appearance I see nothing abnormal. It's a big female.

Additionally the shape of the tail is not that of a musky anyway if someone did some photo doctoring.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.