" She never has a problem with fantasy."
Most people, especially women... have no problems with fantasies. They are quite safe.
For something that you are thinking about - Its more fantasy for you two then it would be for your dad. ie: If I saw my son's wife's boobies (or nude) by accident on a computer or print out, I may enjoy the view for a few seconds and move on. Even thou I'm a kinkster. But that's me.
Now, if the photo had the wife going down on another woman... that would be "jack pot!"
I'm being silly... good luck on working the fantasy... it does make it fun when you can turn it for real.
I had fantasies of eating or fucking while the girl I am with is on the phone with her parents... I've done it a few times. ie: she's naked... picks up the phones, and bla blah blah... just start playing with them.
Ya might get hit for it.