I dunno, I just say "wait there" and back away with my horse. Brock doesn't follow me then. He only follows if I ask him to follow. If he looks at the camera and makes the shot all funky I say "look there" and point him in the right direction, and he does, then I take the photo. I'm a dreadful photographer though, so I'm not sure why I bother lol.
ETA: as far as training them to stay in the one place without holding the lead, I had to do that with Brock because he can undo knots and clips so tying up was kind of pointless if it was going to be longer than 5 mins. I just started by draping the rope over a fence and pretending to turn my back - if he tried to move away I'd turn and say "stay/wait there". Once he'd stand at the fence and not move away even though he knew he wasn't tied I did the same in the middle of the paddock by draping the lead over his neck. He caught on quickly, but he's so lazy he can't be bothered moving around much anyway