My Dear Man,
Take a deep breath and relax. Taking a nude photo of oneself is no crime and he should not have to explain himself to you or anyone else. The more interesting question is why are you so concerned? I would encourage this type of behavior for anyone wanting to know their body better or to keep track of one's progress while dieting or working out. Even if he intends to send the pic to a cyber pal I still see no harm done. Now get out your camera and take a nude photo of yourself and send it to your boyfriend along with a hot proposition for your next weekend get away.
Betty