In many group photos, you don't always know what the others in the group going to do in the photograph. This is especially true when the people in the group are encouraged to make "funny faces".
And it's even more true if you don't know the other people in the photo (which sometimes happen at public events).
Sometimes, that will mean the others in the photo will be making inappropriate gestures in the photo, giving the false impression that everyone in the photo condones that inappropriate gesture.
Just beware of that when you see photos online!
