on-line drawing application

Does anyone know of an on-line drawing application/script/code I can use on a website?

A client wants visitors to be able to effectively draw a picture/logo on their website, save it, then re-edit it at a later time.

I was thinking of something like white board on bebo.com (but with a bit more functionality) or the Mikon Machine at mikons.com (but a little less functionality!).

Anyone got any ideas?