For more information on image file backgrounds, see Image file backgrounds.
To create a 3D image file background
For example, if you want an object in the scene to cast a shadow onto the floor in the background image, create a plane as a stand-in for the floor.
The objects in the scene also appear to cast shadows onto the objects in the background image by casting shadows onto the stand-in surfaces. Consider the following:
To make objects in the scene accurately reflect the objects in the background image
The stand-in surfaces now have the same color as the objects in the background image they represent and the objects in the scene accurately reflect the objects in the background image. However, it also means you have to illuminate the stand-in surfaces properly to make them look identical to the objects in the background image that they represent.