Smudge and Erase Image using Flash and AS3

Hi,
I am developing an app where in I have to smudge and erase a portion of the image which is loaded on stage.

The logic I am using is adding two Images on stage one above the other.

I am able to smudge the image which is in front.

Now I want to erase the part of front Image which is smudged three times and make the Background image visible through that part.

I have made the smudge effect but I am not able to erase the smudged portion from that Image.

Regards ,
Amit Rane.