Or load a prop, or square.
Set its dimentions to something like 240% in X and 160% in Y.
Load your background texture to that.
Then position as required for your render.

If you need shadows, you will have to play with the Ground plane and set it to shadow catch only in the material room.

happy posering

Poser 1, 2, 3, 4, 5, 7, P8 and PPro2010, P9 and PP2012, P10 and PP2014 Game Dev
"Do not drive faster then your angel can fly"!