Actually, it's a high quality panoramic render. But yeah I guess you can call it a screenshot, because it's a picture. To put him behind the screen you copy&crop the sections needed and put them in from of him. Then I recreated the glass separately, made it see-through and blended it until it looked right.
Very nice setting! Love the way Joker's body's leaning against the window except that the accent is more on his right arm than his cute face. And I would have placed him a bit off-center. Nevertheless, when I look at this work of art, I imagine a starry night outside with a gentle breeze caressing his skin. It makes me want to be there with him, about to play Skyllian Blitz with the main crew of the Normandy.