There is another way also.
Use the 2D image on an Alpha plane and use it like a billboard, this can be resized and positioned easily, it also has the advantage of being able to adjust whether you want lights to react with it or not or whether you want it to receive shadows. You can adjust your light parameters not to react to the plane.
I find this more effective than using the camera backdrop myself, but it does depend on the scene you are trying to create, sometimes the backdrop works better!
It's just another choice.

Injustice will be avenged.
Cofiwch Dryweryn.