Create a background image for the Menu

Hello,
I’m trying to create a background image for the menu on my site. When you log in, there’s a menu that has options for “About, Portfolio, Live Performances, Exhibition Photos, Resume, Contact” and then in big letters it says the name of the page you’re looking at. I was wondering if it’s possible to use one of my paintings as the background for just the white space where the menu is. I tried using the background image option but that puts the image behind the entire page, which is too much. Any help would be greatly appreciated. Thank you!

The page I need help with: [log in to see the link]