Create a mask in a movie clip.
Give mask movie clip instance name 'maskMovie'.

On first frame of Scene1:
    stop();
           // mouse.hide();
    startDrag("maskMovie.mask", true);

In mask movie clip 'maskMovie', create a movie above mask layers.
Attach this actionScript to movie instance:
   onClipEvent (enterFrame) {
         _x += (_parent._xmouse-_x);
         _y += (_parent._ymouse-_y);
         img1._x = _parent.img2._x-_x;
         img1._y = _parent.img2._y-_y;
   }