My WordPress site displays featured images at the top of each post. Here's the PHP code from
post.php that generates the featured image.
<?php if ( current_theme_supports( 'get-the-image' ) ) get_the_image( array( 'meta_key' => 'Thumbnail', 'size' => 'single-thumbnail', 'link_to_post' => false, 'image_class' => 'featured', 'attachment' => false ) ); ?>
This code just outputs a standard
<img> tag into the page. For example:
<img src="http://www.ericanastas.com/wp-content/uploads/2015/07/2015-04-10_190211-636x460.png" alt="Parkmerced Block 22 Geometry" class="single-thumbnail featured">
However, other images that I add to the content of a post show as a LightBox when clicked. Here's the HTML for one of these images.
<a href="http://www.ericanastas.com/wp-content/uploads/2015/07/2015-04-10_190211.png" rel="lightbox"> <img class="alignnone wp-image-2770 size-single-thumbnail" src="http://www.ericanastas.com/wp-content/uploads/2015/07/2015-04-10_190211-636x460.png" alt="2015-04-10_190211" width="636" height="460" style="opacity: 1;"> </a>