This should work...however, I didn't test it, and it is late here.
add to modules/Detailed_Product_Images/product_images.php
PHP Code:
$image_check = func_query_first_cell("SELECT count(imageid) FROM xcart_images WHERE productid='$productid'");
$smarty->assign('image_check', $image_check);
Then add to your image template
Code:
{if $image_check >= "2"}
Code to show if there is more than one detailed image
{else}
Code to show if there is one detailed image.
{/if}