for me i did NOT use the CCSM program. it is in KDE menu, System Settings, Desktop effects.
when there, click on 'all effects' tab, then scroll down where it says 'desktop cube'. check it if not already done, then click the 'wrench' icon. then click 'advanced and uncheck 'show caps'. now click 'basic' tab and there is an option for a background color and an option for browsing to use any background image you got. select that and give it the path to the image you want to use as a cube background. once back in basic again, select 'show reflection' and click apply, ok and then you got it
"If you treat your system like a kiln, don't be surprised when a brick comes out the other side."