What on earth is that technique?

I'll start with an easy one:

What on earth is the technique you’re trying to do in that picture? If it’s ude-giri your hand is too high up his arm (pressing down on his shoulder or the upper part of his arm isn’t going to do much), for waki-gatame you’re standing too upright and it can’t be just kote-mawashi since it’s impossible to put enough pressure on the wrist in that position. Besides that kiba-dachi, while traditional, is not a great stance for that position since he can just plant his knee into yours and you’ll collapse, losing the hold. -- Zara

This is reference to a now retired side-bar image, actually taken from a past post and reproduced below:

In Jiu-Jitsu formal stances are typically used transitionally, and are learned in the context of actual application. For example, in this photo I am applying a reverse-armbar -- a restraint and control technique -- from a horse-riding stance:

A reverse armbar

From here I could take Adam down to the ground or move into a more mobile lock to better escort him to the local police station. Either way I would not need to stay in this position for very long.

Of the techniques listed, I'd say it's closest to waki-gatame:

Standing waki-gatame

Think of it as a variation.

The neat thing about the reverse-armbar is that there are lots of ways to make it work. You can lock the shoulder, elbow, and wrist. If you have difficulty with one joint -- typically resistance or flexibility -- you can switch emphasis to another.

In this case Adam has a fairly flexible elbow -- note the hyper-extension -- so I'm using the wrist and using my ulna bone to painfully slice into his upper arm (an alternative to torquing the shoulder - probably more jiu-jitsu than judo!).

As to the risk of his planting his knee: I don't think so! Sure it's a posed shot, but given that I've got the lock and his balance, as he moves I either inflict more pain, stopping the movement, or flow with it into something else.