If the person had time to swing up a camera, focus and snap a pic, they had time to yell, wave their arms, run at the horse and distract him. In fact, that would have been my first instinct, rather than taking the photo.
I was in the paddock when one of our horses went after a barn cat (they usually ignore the cats), and yelling and running at the horse made him swerve; giving the cat enough time to run under the fence.
Nice siggy, by the way. Papillons are too cute!