Okay, that first horse was low in the poll, but he was working through his back and was ON THE VERTICAL which was what I was trying to get at.
I have to say no no no to riders dropping their hands to get the horses on the bit;
always keep your position correct and make the horse come to you. Also, in response to the "there's no command for it" - yes there is. You keep the horse between your legs and ask for them to give to your hands.. I'll explain more below.
Here is a post I wrote back in Feb illustrating how to get a horse on the bit:
There is another way of getting your horse in a frame, and it's a little more straightforward:
You keep your outside rein with contact, then take your inside rein and draw your elbow straight back to your hip, and keep dirivng the horse forward in the gait you're trying to accomplish this in. They may fight and toss their heads around, but with your rein at your hip, the horse will reward itself when it goes into a frame.
Note that both reins should be of equal length.
That horse does look like his head's a bit low! 
