I found someone using dropbox, and, of all unlikely things, the screen slideshow in windows 7. I couldn't make that work, but found something called 'faststone viewer' that will run using a dropbox folder, and automatically update. Then add 'sendtodropbox' and you have a working system!
People not at the wedding can have the dropbox view link. At the wedding, we can set up a system for displaying the slideshow. Very, very proud of myself for solving it!