model.predict keeps predicting the same, wrong, class
Figured it out.  Need to normalize the image I'm going to predict to $[-1,1]$ instead of what-I-assume-is-the-standard $[0,1]$.  It seems this is model-dependent.  The project I'm working off of uses transfer learning and imports this model.
It's not immediately clear to me though just how this model needs inputs normalized to $[-1,1]$.