For your current list, if you'd like to upload a wallpaper you can do:
Profile > Edit > My List Style > Upload Wallpaper / Change My List Wallpaper Settings, and then upload your desired background image. Make sure that "Show Wallpaper?" is set to "Yes".
If you want it to look like mine, where the image is more visible, then you will have to edit one of your personal list styles. If you haven't already done so, you can make up to two personal list styles which you use to make your own unique list designs. Do Profile > Edit > My List Style > Advanced Style CSS Editor (and then create at least one list ID to work with if you haven't already made one). Go back to Advanced Style CSS Editor and click on one of your personal list style ID's. You can use my style for now. I plan on making a tutorial later which will explain how to make one from scratch.
Copy everything in the spoiler below and paste it into your personal list style ID.
Then click "Update CSS".
Now for your desired background. Go into editing mode for the ID you pasted my stuff into. Look where it reads:
background-image: url(
http://i.imgur.com/nhavo.jpg);
Within those parentheses, paste the image url of your desired image in place of mine. If you want to know of some places where you can upload images to, let me know. Once you've uploaded your image somewhere, you can just paste it in, and there you have it.
Oh, note that you may need to resize some images. If an image is very large, some of it may be visible but some of it may be hidden behind your list. (I recommend just uploading it, testing it out, and then if you see that it is too large, edit it as much as you need to). (If you need to know a place where you can resize images, let me know). Also, this is pretty important too if you care about detail. With the code I've given you, you may only want to use images that have white backgrounds. If you upload a wallpaper or something with a black background, it won't appear as mind does. My image appears the way that it does because it has a white background, and I have made my list have a white background. So they work together. You can do the same with an image that has a black background and a list that has a black background.
If your list has a white background and you upload an image that has a black background, the black will be noticeable and it won't look natural.
