Access images within the library

I need to be able to access the actual image from the library so I can do this:

function drawShape() {

    console.log('draw shape');

    overlay = new createjs.Shape();

    stage.addChild(overlay);

    overlay.graphics.clear()

        .beginBitmapFill(img)

        .drawRect(0,0,800,600);

  overlay.cache(0, 0, self.canvas.width, self.canvas.height);

}

var img = new Image();

img.onload = drawShape;

img.src = "test.png";

Do anyone know how to grab the image from either the library directly or from an MC holding the image?
Just to be clear I need to the actual image file so I can manipulate it directly. Simply loading an MC containing the image or loading the image via linkage will not work. Not unless I can use either of those to grab the image.