Hello.
I’m having a similar issue.
I’ve just upgraded to the Twenty Thirteen theme but the only thing it is missing is the ability to choose your own background (otherwise it just appears blank).
I tried the method detailed above but it doesn’t seem to work for me?
My site is Eclectic Relaxation (eclecticrelaxation.co.uk) and this is the picture I want to use (http://eclecticrelaxation.co.uk/wp-content/ERBBackground5%20(faded).png).
Any help would be greatly appreciated!
