I made a movie slide show using Windows Live Movie Maker.  I had edited some of the photos, using Windows Live Photo Gallery,  before including in the movie---and I notice that with each playing of the movie, some of these photos enlarge so that I am losing the tops and bottoms of the pictures.  How can I prevent this?

Also--how can I learn more about the size of original and cropped photos in general---seem to have a lot  of variation and I don't understand all factors involved.