Sorry for the late response on this question :(
The jBPM console overlays divs ontop of the image in order to display the red arrow icon next to active nodes in your process. Here is some sample code that does this:
String s =
"<div style='width:1024px; height:768px; background-color:#ffffff;'>" +
"<div id=\"imageContainer\" style=\"position:relative;top:-1;left:-1;\">" +
"<img src=\""+imageUrl+"\" style=\"position:absolute;top:0;left:0\" />";
for (ActiveNodeInfo activeNodeInfo: activeNodeInfos) {
s+= "<div class=\"bpm-graphView-activityImage\" style=\"position:absolute;top:"+ (activeNodeInfo.getActiveNode().getY()-8) +"px;left:"+(activeNodeInfo.getActiveNode().getX()-8)+"px;width:50px;height:50px; z-index:1000;background-image: url(images/icons/play_red_big.png);background-repeat:no-repeat;\"></div>";
}
s+= "</div>" +
"</div>";
Hope this helps.