header.php

<?php
if(is_single() & !is_home()) {
  $myfield = 'PostTitle';
  $postimage = get_post_meta($post->ID, $myfield, true);
?>
  <style type="text/css">

    .entry-title {
        border:none;
        color:black;
      <?php
      if($postimage) {
      ?>
        background-image: url('http://letthemstare.com/wp-content/themes/manifest_v1.1/images/<?php echo $postimage; ?>.jpg');
      <?php
      } elseif(!$postimage) {
      ?>
        background-image: none;
      <?php
      }
      ?>
    }

  </style>
<?php
}
?>