On this page, you can see plenty of cloud formations in some lovely skies.
If you like one of these images and want it as your wallpaper, just click on one of the links below it (eg 1024x768) and you can download it to your computer. Where you save it to on your computer so that you can use it as wallpaper depends upon your system...
On Linux with KDE, you can just save it in your Documents/Pictures directory or, if you want everyone to have access to it, there should be something along the lines of /opt/kde/share/wallpapers that you can share it in depending upon versions and level of choice exercised by your admin (if you have access to that part of your system that is).
Note that the copyright on these pictures remains at all times and in all respects the property of me: Paul Grosse. You are licensed to use these images only on your home machine and only as wallpaper - you cannot modify them or use them for anything else.