I would like to display a fully opaque image (e.g. PNG RGB8) on the desktop in an image viewer - but such that I can set the window (showing the image) to be, say, 50% transparent (so I could see through and compare with other windows below). It would be even better if the viewer just shows a "panel" instead of a "window" (i.e. I'd prefer just the image shown, possibly with a border - instead of a full blown window with menubar, titlebar etc).
I'm aware that in Compiz, it should be possible to run a plugin, and have any window you want transparent - but I was hoping for a solution (viewer) that would not be Compiz-specific (and even more preferred, if it is neither Gnome nor KDE specific - but I'm not sure that is possible). ...
Any suggestions for an image viewer like this?