Thanks for the replies everyone.

I think most of you are missing the point though (lesbentley being the exception).

My question is not "how do I make a background picture?". My question is "why doesn't it work when I plug in a picture node to my background and render ?"

It is meant to work, and this is supported by the fact that it has worked for lesbentley. Why is it not working for me ? The only change that I have made to copy lesbentley's setup is to change the color attribute to be the same as the BG shader. It still stubbornly renders "all white".

I've attached an image of my settings.