Rotating a dynamically-loaded image

Will someone please tell me how to rotate about the center an image loaded dynamically through AS? I’ve already asked this question, no one answered, I searched, searched some more, looked through my fairly voluminous collection of example flas and have come up with nothing.

The following code does rotate a mc about its center, but only (apparently) if the mc contains something when the swf loads. I’d really appreciate some help here.

    this.rotation_speed = 2;
    function origin(){
        var bounds = this.getBounds(this._parent);
        return {x:(bounds.xMin+bounds.xMax)/2, y:(bounds.yMin+bounds.yMax)/2};
    this.rotation_origin = origin();
    this._rotation += rotation_speed;
    var curr_origin = origin();
    this._x += this.rotation_origin.x - curr_origin.x;
    this._y += this.rotation_origin.y - curr_origin.y;