I'll take a look at it tomorrow. Meanwhile, you could use the ScriptPanel and simple draw the image there (the ScriptPanel is working correctly, I am using it for another iPad project).
const var Panel = Content.addPanel("Panel", 0, 0);
// [JSON Panel]
Content.setPropertiesFromJSON("Panel", {
"width": 1024,
"height": 768
});
// [/JSON Panel]
// Load the retina image with double resolution
Panel.loadImage("{PROJECT_FOLDER}bg.png", "bg");
Panel.setPaintRoutine(function(g)
{
// name, x, y, w, h, xOffset, yOffset
g.drawImage("bg", [0, 0, this.getWidth(), this.getHeight()], 0, 0);
});