For more information on image file backgrounds, see Image file backgrounds.

To create a 3D image file background

1. Create an image file background for the perspective camera you plan to render from (see Create a static image file background or Create an animated image file background).
2. Use the background as a reference to create a relatively simple surface or group of surfaces to act as stand-ins for the objects in the background image that you want to interact with the objects in the scene.

   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.

3. Scale and, or position the stand-in surfaces so that they are directly over the correct areas of the background image.
4. In Hypershade, select Create > Materials > Use Background, and assign the new material to the stand-in surfaces. The stand-in surfaces have the same color as the objects in the background image that they represent.
5. You can now make objects in the scene appear to move behind objects in the background image by moving them behind the stand-in surfaces.

   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 background image appear to cast shadows onto objects in the scene, in the Render Stats section of the stand-in surfaces’ Attribute Editor, turn on Cast Shadows.
   • To make the objects in the scene appear to accurately reflect objects in the background image, in the Render Stats section of the stand-in surface’s Attribute Editor, turn on Visible in Reflections. Visible in Reflections is on by default.

To make objects in the scene accurately reflect the objects in the background image

1. Assign a Blinn or Phong material (for example) to the stand-in surfaces. Do not use a Use Background material.
2. Map a File projection texture to Color—right-click the File texture to select Create as projection when applying the texture in the Create Render Node window, or if importing a file, select As Projection from File > Import.
3. Map the background image to the Image attribute, set Proj Type to Perspective, and set Link To Camera to the camera with 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.