I am new here. I chose Zenphoto because it seems to have rich features but is easy for the end user to use...now just have to get the admin up to speed! I would like to be able to view very large thumbnails of the pictures while browsing, but I want (hope) that the file size could be small to facilitate the loading time to view a photo. Is this possible?

The big picture: I teach a yearbook class and need to have all of my photos available for all of my students to browse and choose from, but our internet connection is a bit slow. Please feel free to correct my terminology, if I am using the wrong words.

On the front end (Theme) you can have bigger thumbs. You can change the size on Options > Theme.

But not all themes allow changing the thumb size for layout reasons though. The basic theme does, the Zenpage theme does not for example. In that case you would have to modify the theme itself. Here is some reading about that but depending on your knowledge it might be a bit technical: http://www.zenphoto.org/news/theming-tutorial/