One thing to keep in mind is that the Display and DisplayCanvas use the information about the currently displayed (
-)image to scale the overlays correctly (the overlays are displayed in image coordinates, see also How to use Overlay and mouse click with WPF display (c#)). Conversely this means that if there is no image currently set on the Display.Image or DisplayCanvas.Image you won’t see anything because the display/display canvas does not actually know how to scale your overlay.
I’ve put together a very quick and even more dirty demo that shows the concept. Note that it’ll need TwoWay binding on the selected rectangle to work properly. SimpleDemo.zip (466.4 KB)