ACW
Don't want to prolong the 'don't do it without training' comments because they are all correct. For reasonable air to air photos you dont need to be in close formation but you do still need to get some training and make sure you are flying with a photo ship pilot who knows what he is doing. In some ways photo work is more dangerous than close formation as you tend to be changing position quite a lot and trying to get interesting angles.
I have flown quite a few photo sorties but always with a known photo ship pilot, a known photographer, and a pre flight briefing. It is great fun and we work as a team to get the best shots possible to show off the characteristics of the aircraft in question.