You can pass the image url as a href attribute=> file:///Users/me/Documents/my_pic.jpg directly within your xml. It just needs that you pass a local, static and valid url.
If you want to add image later once the xml is flowed and so target specific nodes and inject images, it's a bit more complex. If the node is not part of the layout, you may try to reach the XMLElement objet and such an attribute, then layout the element.
var x = some XMLElement
If already placed, then you have to get the associated pageItem, then place your file into it.
pagItm.place ( File ( "/Users/m/Documents/my_pic.jpg" ) );
Hope that helps,