I noticed there are a number of scripts listed under photo galleries that specialize in wallpaper over at hotscripts http://www.hotscripts.com/PHP/Script...ies/index.html
You might want to install a forum like vbulletin, and then do some extra customization to show thumbnails of the latest wallpapers and most popular wallpapers. And maybe you could even have links for your users called My Wallpapers.
You can use wallpaperscript v2.02. It is best wallpaperscript:
W-script is a full featured wallpaper site creator script. It takes minutes to setup and start earning money from your new website. If you need a serious script to manage your wallpaper site like a PRO then W-script is the right solution, in front of the average competition with giant steps.
If you don't mind paying some small amount of $ thank you can also use Wallpaper Site Creator from CollectPHP or if you can invest some more money then you can look after "Wallpaper Script" (wallpaperscript.com).
Have a look at that HotScripts category. Lots of them will do you, and you could easily add some AJAX in for smoother viewing.
If you check the descriptions you'll notice several allow you to set users at different contributor levels, hence they can put new pictures into different folders, pending different levels of moderation.