Below we are only using 5 main 300x300 images and don't need any thumbnails. They are reduced by the browser to 75x75 and then resized to 80x80 when the mouse passes over. The browser does the resizing so it's not as smooth as a graphics package would produce. Below are 5 75x75 thumbnail images that are expanded by JavaScript to 80x80 when the mouse passes over. So we need 5 main images and 5 75x75 images.