It took a lot of research, but I finally found a widget plugin, Daiko’s Text Widget, that will let me insert an image in my sidebar. Check it out live at my blog, Jimboland Jots, at http://www.jimboland.com, at the top of the left sidebar.
You’ll need to download and install his plugin, activate it, and then create an image link with an absolute path to the image you wish to display.