I would add this to the photo-album package, which allows you to call /packages/photo-album/www/slideshow via include that takes album_id as an argument and popup_p, random_order_p, refresh_rate.
If popup_p is true, a new window would open with the pictures of the album_id shown in random_order, refreshed every regresh_rate of seconds.
If popup_p is false, include a back and forth button at the bottom of the picture, that will (on_submit) go one page forward or backward, while keeping all the values of the surrounding page. Not even sure if this is possible, maybe you can do some java script magic with embeded elements, but it might stress the capabilities of HTML.
Alternatively, just display all the pictures below each other (if popup_p is false, that is ;)).
