You've put a tag of "wbs" on your question so I assume that is the diagram type you are interested in.
Did you know you can define custom sprites?
If you download the Plantuml.jar and double-click it then you get a basic GUI. And (today I learnt!) in that GUI there is a File->"Open Sprite Window" that will automatically convert any image in the clipboard and output a range of definitions for using that image as a sprite (at various resolutions and colour scales). Note that for large images it can take several minutes to process (during which the window seems hung) and some of mine ended up as bad sprite definitions - best to keep the image small.
So I created:
(click for online server)
How close is this to what you wanted?