Poser - OFFICIAL F.A.Q (Last Updated: 2021 Sep 23 9:32 pm)
Place it on the One Sided Square and scale to fit. You can make the thing as big or small as you please.
IMO, there are much better ways to use pre made backgrounds in Poser than putting them in the scene while you render, but that's a whole nother thing.
Coppula eam se non posit acceptera jocularum.