Keep in mind that I'm a novice at this environment but I don't see why the DragDetected event would fire. It is linked to the 'ivSource' imageview which has nothing in it to be dragged. I tried giving it an image in the Designer and then trying to drag that image around. When I did, the image dragged and the event fired as expected.
As for dragging an image file from the desktop to the ivTarget imageview, it worked fine for me.