Display all images attached to a post in WordPress (http://tommaitland.net/2012/10/display-all-images-attached-to-a-post-in-wordpress/)

snippets.php

<?php
$gallery = get_children( 'posts_per_page=5&post_type=attachment&post_mime_type=image&post_parent=' . $post->ID );
$attr = array(
    'class' => "attachment-$size wp-post-image",
);
foreach( $gallery as $image ) {
     echo '<a href="' . wp_get_attachment_url($image->ID) . '" rel="gallery-' . get_the_ID() . '">';
     echo wp_get_attachment_image($image->ID, 'thumbnail', false, $attr);
     echo '</a>';
}