I'm guessing it's something so simple I'll be embarrassed to find out.
The way I've added them to my text box is to find an image online - copy the image - then paste the image into the text box. I tried again, and it still works. That will not work, however, copying an image from your computer.
To place an image in the author's note section requires using an embed feature. Something like this, which I used with a poem focused on a photograph by Diane Arbus. The image appears in my author's note section.
<img src="http://www.artandcointv.com/blog/wp-content/uploads/2012/03/dianearbus.jpg"height="233" width="390">
Many thanks, Sam. I'll try it.
It worked! Copied from Google images.