you put it as an image plane on your camera.
Camera attributes>> evironment>>image plane >> create
But you dont want to do that, you want to render your elements with an alpha channel and then composite them onto the background in another program. The reason being that if you render your images with your background then you can't change them, you would have to re-render everything again. Also you wont be able to make lighting tweaks etc to the cg elements in the image without affecting the background. Also rendering with a background in slows your render considerably.
Alan
Technical Director - Framestore
Currently working on: Your Highness
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