Much in the way we did with xfce here is the way to implement de auto change feature in KDE.
This is an easy one. Although you can perform background auto change from KDE control center, it may be usefull to have a script to do the task. You can use this script to create a [...]

We need three files for this:

signature.txt: you should point your mail client to this one
signature.tpl: here is the common text to display, something like “xmms is now playing:“
signature.sh: the script first copies the contents of the template file to the final signature file, and then adds the current song as a new line.

First of all check Xfce 4 Desktop Manager help. Click on the New list… button and create a list with all the backgrounds you want to rotate.
From this page:
To refresh the backdrop with a new random image from the list just run the xfdesktop command again, e.g. from a terminal or the run dialog, or [...]