I display several small graphic pictures on top of my desktop.  Using LXDE under Ubuntu or Fedora display the image correctly.  Under XFCE in either system, an icon is displayed instead of the image.  For example I have a png file of a picture of Tux with my user registration (50887) which displays correctly under other windows managers, but not under XFCE.  It displays an image of a monitor with PNG on the screen and the number beneath that icon as if clicking on it will do something.   I converted the image to a jpg with gimp, but the jpg does the same thing. 
I run a 64 bit system and a 32 bit system and both have the problem under XFCE.  I have tried Fedora 15 and 16 and Xubuntu and get the same result.  When I switch to another window manager, the problem goes away.