Try using a program called FotoSizer, (you can find it here: http://www.fotosizer.com/) It will take one or more images or a folder or folders (the loading process is not fast, but it's acceptable). The % option works best for mixed images (portrait and landscape).

Thanks Ken, this is the sort of utility I was looking for.  I won't be able to try it out for a couple of weeks but will circle back and give it a try.