This modification will generate and resize small, medium and large images automatically when you upload the large image to the server. It also allows you to have larger images displayed when mousing over select smaller images. It will also allow you to watermark images and upload additional images for products through your admin interface.
GD Libraries or ImageMagick must be installed on your server for this modification to work.
Zen Cart Version 1.3.9, 1.5.0, 1.6