I have switched to Xubuntu a few months ago coming from Kubuntu. I liked there the (already available) option of setting up a list of image files and have them randomly displayed. This was one of the things I have missed so far in Xfce.

As former Windows user I have aquired quite a large number of wallpapers (thx goes to HTTrack for downloading over 18k wallpapers...) and I like to have them displayed on the background. That's more or the less the only major change I do on a theme (if you can call that a change...)

Anyway, thx to TheSheep from the #xubuntu channel on irc.freenode.org (he's a really helpful guy and has helped me countless time) I can provide you with this small howto.

(1) Build your list of images
- Right-click on your desktop
- Select "Desktop settings"
- Make sure that "Allow Xfce to manage the desktop" and "Show Image" boxes are checked (they are by default)
- Click then on "New list"
- Add the image files by clicking on the "+"
- Once you are done, save the list
- You are back in the previous screen and your newly created list should be selected in the "File" input box
- Then close that interface

(2) Creating Cronjob for Wallpaper Changer functionality
- Open a terminal
- If you already have a "cron-command" file for your user, open that one in a text editor if not execute this command: nano cron.txt
- Enter the following two lines to the cron file:
# Reload Background Image
0,5,10,15,20,25,30,35,40,45,50,55 * * * * killall -USR1 xfdesktop
This will change the image every 5 minutes. You can also change the behaviour. Please refer here: Cron HowTo
- Exit nano by pressing ctrl-x
- Press [y] to save the file

(3) Adding the Cronjob for Wallpapcher Changer
- Before you overwrite any existing user cronjobs please execute this command:
crontab -l
If nothing is returned then it's fine to add you wallpaper changer script!
- Add the cron.txt file that we created under section (2) by issuing the following command in the shell:
crontab cron.txt
- Enter now again crontab -l and you should have this output:
hyper@xubi:~$ crontab -l
# Reload Background Image
0,5,10,15,20,25,30,35,40,45,50,55 * * * * killall -USR1 xfdesktop
(4) That's it
- Get some coffee or whatever and enjoy your desktop bakground wallpaper changer