I didn't get a chance to save the edit. As soon as I released the mouse button, Chrome rendered the image in the browser window and displayed its path and filename in the address bar. Maybe holding down CTRL or ALT or something would work...didn't try it.
Or maybe just copy and paste. I guess I should pay attention next time and make a tutorial of it.
Better still, Mark should get around to putting the Add Pictures button on the formatting toolbar, to be consistent with Messages. ?