I searched the forum using Google and came across a few threads like http://www.sitepoint.com/forums/showthread.php?834646-Best-CMS-for-Galleries and http://www.sitepoint.com/20-gorgeous-wordpress-gallery-themes/
Now I need to ask: would you recommend anything else than wordpress (it's kind of hard to create a design for it, i am not a programmer) and if yes, what?
Second of all, is it possible to mass add the wallpapers to wordpress? Adding them one by one wouldn't be practical.
Wordpress is actually one of the easiest platforms to create a theme for.
Drupal also gets a strong recommendation as a CMS, but the templating system is slightly more complex than wordpress. The reason why wordpress is so popular is because it's simple to use and develop for.
If you use something other than IE to access wordpress, then yes, there is a mass drag-and-drop upload feature available (on the back end). However, you will be encounter the PHP upload filesize limitation on the server.