I didn't post this as a Custom Box BG before because I posted it as an expirament for me to try
well what can I say, it worked! So here goes
If you're a Premium member you can use this in the background of your "Custom" boxes [link]
This will show you how
The trick that worked for me is under the "Direct link to image location" what you need to do is right click the image and then click "copy image location" and then paste it into the "direct link to image location"