Get Image based on Sort Order

Question

I am trying to change the image on hover for product in listing page for one of our Magento Eshop. I can change the image on hover. What i did was i used small and thumbnail image for it and changed it using mouseenter and mouseleave event.

But now i want to change it based on sort order. Say the image with Sort Order 2 should be visible on hover.

I am not sure how to do it ? Could anyone please guide me on this. From where shall i start ?

Thanks