Using whatever lineTo(); draws as a mask

How’s it going fellow kfians. The effect I would like to create is as follows: I have an image movieclip named “myImage_mc”, and I want to create a spray paint effect, where the user “paints” whatever myImage_mc is using the lineTo and lineStyle commands. I have the lineTo stuff all done, the problem i have is trying to make whatever the user draws a mask that shows the image.

Here’s my code so far:

this.onLoad = function() {
    _root.createEmptyMovieClip("empty_mc", this);
this.onMouseDown = function() {
    empty_mc.moveTo(_root._xmouse, _root._ymouse);
    drawIt = "true";
this.onMouseUp = function() {
    drawIt = "false";
this.onEnterFrame = function() {
    if (drawIt eq "true") {
        empty_mc.lineStyle(65, 0x000000, 100);
        empty_mc.lineTo(_root._xmouse, _root._ymouse);

The movie is set up pretty basically so far, two layers, top one contains the above as, and the bottom one contains the image movieclip named myImage_mc. Any ideas? is this even possible?