I like this idea. I would more than happily write this on invitations. People write “No Boxed Gifts” and that is respected. I really would not want people taking pics on their cameras/phones and then sharing with the world. If I wanted the world to see my wedding, I would invited the world so to speak. My day would be my day with my close family and friends and a few odds I would HAVE to invite to be polite, why do I need to risk it being shared with the general public on FB/Youtube and other sites.