Creating a scratchy ticket

Looking to create a scrathie ticket effect in javascript where a block is presented and you with the mouse) click and drag to reveal the image behind

Am determined not to use Flash

This is the best I could find so far in terms of an example script http://www.siteexperts.com/tips/styles/ts37/page1.asp

Anyone know of a better more 'scratch-like' example with code?

Best bet would be to overlay a canvas over something, and scratch away the position of the mouse pointer.

jsFiddle.