Scratchy Card?

I need to make a scratchy card type thing.

Basically three boxes appear, you click and drag to scratch away to reveal the picture behind each box.

There are loads of flash sites around doing this. Tacky as hell.

Just wondering if anyone knows a way I could do it with Javascript, that’d still be compatible with ie7.

I’m not an expert JS coder but if there is an example around I could probably mod it to my needs. Haven’t found anything yet.