Using CSS to Place an Image at Bottom of Page

On my site (zdroyd.net) I am trying to place a image, background image, at the very bottom of the page. HOWEVER the image will be behind the text, in the exact same way as the image at the top of my page.

Can anyone tell me how I can do the exact same thing as I did on the top of my page (placed an image with a “wrapper class” so that the image would act as a background and be rooted to the top) but instead have the bottom of the image be at the bottom of the page.

I have googled everywhere and no one gives a working example, I know how I could do it if it was a static page, however the page is likely to change the size because of the wordpress loop being present.

I would be really grateful if someone could give me a straight up answer, and not just point me at a random page that does not help.

Thanks,

Zdroyd