Most people, and certainly first-timers, have zero clue if or when their photo is going to be taken on a ride. It took more than several rides on the photo rides for us to even figure out where the cameras were. I am not "guilty" of the hand-throwing crime as I'm typically white-knuckling any bar that has been provided for me to cling to, however, throwing one's hands in the air is a natural and common reaction when experiencing a ride drop. As others have suggested, if the ride photo is that important to you, ask for the front row. Even then, you can't control the reactions or faces others will make on the ride.