Online collaborative drawing program

[Len Padson]

Hello! I am trying to create a networked collaborative drawing applet, and I'm looking for suggestions as to the best, easiest, most efficient way to do so. To start, the only functionality I want is to be able to scribble on a canvas, so what should i send from the client to the server and then from the server out to all the clients? should i send the whole image? Should i send coordinates of the points drawn most recently? Or is there some third option that would be faster? I do not want to end up with an ArrayList of every coordinate of every line becasue then as time progresses response time will get slower and slower. So please help? Thank you!