This is an example of an incredibly disturbing photo bomb. Some people just can't help themselves when it comes to photobombing. If the opportunity is there, they'll take it. They'll take that opportunity even if their loved one is taking a very important picture and would be horrified to later find your naked body in the photo. This is why it's good to have friends who know how to use photoshop. They could zap him out of that shot in a minute or two.
This could be like the poster for a horror movie called, 'Photobomb.' I can see the trailer now. The person taking the picture says, "your dad is photobombing in the house." The girl would look confused and say, "that's impossible. I'm home alone." That's when the girls realize that all of their photos have a mysterious photobomber in them. Ooooh. Spooky.