No, that's part of my template, though the box is only supposed to be around the image, not the larger image link. I'm guessing that lightbox 1.3 modifies includes/templates/YOUR_TEMPLATE/templates/tpl_main_product_image.php.
But anyway, details on how to remove the drop shadow are in the readme.txt. All you have to do is remove the section of css that controls it (bottom of the main stylesheet).
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