Thanks, Isaac. That's helpful. I did play with Labeled yesterday when I was trying to get something to work with my actual problem, which involves a Manipulate, ListAnimate, GraphicsGrid, Show, and ListPlot. I didn't have any success with that, but I never tried Labeled with the simple Circle and Rectangle example I provided. Today I was "pretty much" able to get Labeled to include footnotes for that (some formatting issues remain).
I'm kind of surprised that Mathematica seems unable to build interrelated graphics and then treat the entire assembly as a unit that could have notes attached. Perhaps it's time for Footnote[expr, ... ] or some such thing.
Thanks, again. I very much appreciate your help. ... Gary