Haha this is such a fun post! I can't really see the face to well but I know exactly what you're talking about. There's this really funny picture my dad took way back in the day when I used to be big into running half marathons. He thought he was just taking a picture of me running but it wasn't until later that we discovered me and 2 other people were in a perfect line making the exact same hilarious face with our mouths open in a big O shape. Not quite the same as maybe finding something creepy in the background but still funny none the less to find something you didn't expect.
Photos can be hilarious at times. I saw a post on Facebook the other day that showed people who accidentally wore the same colors or looked like dopplegangers in stores, etc. It was pretty funny. I wish it would have allowed the photo to be blown up bigger, so you could see it. It was an odd shadow on the glass.