I can remember back in the day of the Droid X one of the big features in custom roms was always a customized notification panel background. Most developers would theme the background to include their logo or some image that represented their rom. Once this became popular developers found ways to allow users to customize this themselves. Before the option was baked into various roms you would have to use an app like "ninjamorph" to tear down the Framework.res so that you could replace the notifications panel image with your own. These days full blown images in the notifications panel have been pretty much replaced with transparency which tends to look much cleaner and less cheesy.
If however you would still like to add a bit of swag to your expanded notifications panel developer "serajr" may have the xposed mod for you. His new Blurred System UI mod allows you to Blur the Expanded Notifications Panel for a custom look. This mod includes plenty of settings so you can get the effect just right for your setup. You must be rooted and you must have the Xposed Framework installed on your device to use this. If this sounds interesting to you head to the link below for the download.
Via XDA