There's some program I used to use. I forgot it's name. You can configure what will be time's interval between changing wallpapers, where to took these wallpapers from (there's original cool website), etc.
@ BountyHunter: I found a link with some wallpaper changer programs, maybe some of those names will remember you the exact program.
The link is this, http://www.ethow.com/2013/01/change-desktop-wallpapers-automatically.html
Otherwise, you can try to search in google and looking to some names of those programs that you may remember the name somehow.
This is how the desktop of my main pc looks lately:
The games in the bottom left corner are not really the games I play. They are just the games that created desktop shortcuts
@ ohaz, The Gajos: Ye, I bet it's an awesome game. I've never played any of them but I definitely will as the 6 witcher books I've read were awesome (although Ciri is portrayed a lot more mature in the wallpaper compared to the book cover).