One way to do this, but perhaps not the best, would be to
create a draggable MovieClip. Let's call it mcPenny. On a layer
below the mcPenny's layer, you create a small silver MovieClip (2x2
pixels). Call this mcMetal. Make a dense grid of the mcMetal
MovieClips, giving each a different instance name.
Perform a hitTest between the mcPenny and each of the
mcMetals. If any of them are in collision, make the visibility of
the overlapping mcMetal false.