I've got this installed on two sites and have the same issue on both. It seems to work fine on some pages but not others. For example, http://www.zen-cart.com/modules/ipb/...howtopic=46701

IH2 works on the images in the upsell and cross sell boxes at the bottom of the page but not on the product image. On the home page, IH2 does not on the images in the best sellers box but it works on the images on the category pages.

I assume it's supposed to work on the product image, right?