>the Canvas object in HTML 5 contains alot of great things
one of the interesting things is that it has a implemented method to get the data inside the canvas as a base64 encoded string.
So if you would
var img1=new Image();
var img2=new Image();
Data will now contain a png image with both the images.
Encoded using base64 easy to send using ajax or store in a field.
You can draw images, plot dots, draw lines, boxes.
There is some online painting sites that already is using this.