Ok...so I've ruled out that this is unique to my site. A portion of the code I posted in post 2409 can be found in this file:

includes/templates/my_custom_template/templates/tpl_modules_main_product_image.php

The code is below:

Code:
<script language="javascript" type="text/javascript"><!--
document.write('<?php echo '<a href="' . zen_lightbox($products_image_large, addslashes($products_name), LARGE_IMAGE_WIDTH, LARGE_IMAGE_HEIGHT) . '" rel="' . $rel . '" title="' . addslashes($products_name) . '">' . zen_image($products_image_medium, addslashes($products_name), MEDIUM_IMAGE_WIDTH, MEDIUM_IMAGE_HEIGHT) . '<br /><span class="imgLink">' . TEXT_CLICK_TO_ENLARGE . '</span></a>'; ?>');
//--></script>
<?php } else { ?>
<?php // eof Zen Lightbox 2008-12-15 aclarke ?>
<script language="javascript" type="text/javascript"><!--
document.write('<?php echo '<a href="javascript:popupWindow(\\\'' . zen_href_link(FILENAME_POPUP_IMAGE, 'pID=' . $_GET['products_id']) . '\\\')">' . zen_image($products_image_medium, addslashes($products_name), MEDIUM_IMAGE_WIDTH, MEDIUM_IMAGE_HEIGHT) . '<br /><span class="imgLink">' . TEXT_CLICK_TO_ENLARGE . '</span></a>'; ?>');
//--></script>
It appears to be calling both the large and medium product images from the default zen cart locations instead of from the bmz cache folder (which is where images reside when IH2 is installed).

Neistudio, I know you mentioned being unfamiliar with IH2, but is this something you would know how to change? In other words, if you know how to write code, is it easy to change where the images are called from, or is IH2-specific knowledge required? (the bmz_cache folder resides at the store root).

I would do this myself and submit the changes here for the community, but I don't know how to write the code.