<div class="related_posts">

<?php

$my_query = new WP_Query('orderby=rand&numberposts=4');
  while ($my_query->have_posts()) : $my_query->the_post();
  $do_not_duplicate = $post->ID;
		$src = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), array( 5600,1000 ), false, '' );
		$thumbnail = get_the_post_thumbnail($post->ID,'thumbnail');
  ?>
  <a style="background: url(<?php echo $src[0]; ?> ) !important; background-size: cover !important;" class="post" href="<?php the_permalink(); ?>" title="<?php the_title(); ?>"><span><?php the_title(); ?></span></a>
<?php endwhile; wp_reset_postdata(); // End the loop  ?>


</div>