Pagination in Zenphoto is integrally built into the normal way Zenphoto works (loading pages via the index.php script.) You will need to pretty much setup the "normal" Zenphoto environment. Seems to me that you would be better off just using that environment in the first place.
Anyway, since it seems you are not putting album thumbs on the page you do not need the `normalizeColumns()` part. You can use just `next_image()`. You will also need to manage the Zenphoto page# variables.