That is really odd.
It's not every photo, I'd say it is about 50%. It's done it on every iPhone I've had going back to the 6s Plus. I specifically remember trying to figure it out when I had the 6s Plus.
It's happens really fast so you have to be watching for it.
Can one of you post a video? Just want to make sure of this before contacting Apple. All the video needs to do is show you click on say 3-4 images under Google Images. It happens when the photo first opens. This is boggling my mind
Appreciate you both responding.