Erase tool MovieClip.graphics.lineTo

Hello :). I have one simple app, loads an image and then via class that extends shape the user is able to draw. Now I want to create an eraser tool so the user could erase something that he dislikes. As far as I know the easiest way is to make:

lineStyle(size, 0xffffff,1);
                    moveTo(mouseX, mouseY);

and if the background is white I am ready. However it is not and I don’t know what to do. Have you come across this issue before? Thank you in advance