If you’re creating your own WordPress theme and want to pimp photo galleries you will probably use a Lightbox plugin like Simple Lightbox, wp-jquery-lightbox or WP Lightbox 2. If you’re not very familiar in creating WordPress themes in addition (like me) you might forget the following lines and wonder why linked photos aren’t showed up in the expected overlay.
By using another theme on your website you can easily detect whether you forgot something while coding your theme. If the overlays are working with another theme you might forgot the following lines:
<?php wp_head(); ?>
<?php wp_footer(); ?>
In my case the issue was fixed by inserting the mentioned lines. 🙂