WPF windowformhosts transparency issue

We are using a third party control that requires a WindowFormHosts.(map)

We would like to have the ability to overlay custom marker images.  The marker images act as a location point on the map.  It seems as though there is no way to set the transparency of the image once it is drawn on top of the map. 

Picture Box, Label or Panel all appears on top of the map but not transparent any help on this would be appreciated.

We have a map control that must use a windowformshost control.  We then use user control to represent map markers(points on the map) which is a windows forms picture box that has an image loaded into it. What happens is that the image appears on top of the map (windowsformshost) but the background of the picture box is gray not transparent. (bing,google)

Example: http://www.gregmc.com/gmcinc/windowformshost.htm