Ideally it should be possible to display data:images inline with code along the lines of below, but it doesn't seem to work. When I tried it, I got a broken-image icon in the preview and an error message when I tried to post anyway.
< img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==" />
(ignore the spurious space between < and img, the broken-image checker is apparently overzealous and backslash escaping doesn't cut it)