If you are a registered user of these forums, you can upload images to the Gallery. Post your own fan art or wallpapers there and make a post about it in this forum to give yourself some publicity. We also make weekly posts on the site main page, pointing out new additions to the gallery.
Please don't put 6 or 8 versions of the same wallpaper, in a variety of sizes, into the wallpaper gallery. The best way to do it was pioneered by HolyKnight, and we recommend it. Make the wallpaper in a variety of sizes/dimensions, and upload all of them to your personal user gallery, with just one (the largest) in the main wallpaper gallery. Every image you upload goes into your user gallery; images will also go into the other galleries if you specify that as the target when you upload them. (Be sure you put one version of your wall into the wallpaper gallery, or else no one will see it in your member gallery.)
If you want to make it easy for people to appreciate your work, put links to the various sizes in the caption of the one you put in the main wallpaper gallery. For example. Also note that you can create subfolders in your user gallery to organize your work. Check out HolyKnight's, for example.