There is no documented way to do this.
You can take advantage of the fact that text cells will be interpreted as HTML if they are in the proper format, such as
Using that I have been able to get the "broken link" icon, but I have not yet been able to get an actual image up. And you have to do nasty things to cell widths and fontsize to make room for the image.
If there is a mechanism for this, it would probably be described at Yair's undocumented matlab site