function feature_thumbs() {
if (is_home()) {
  global $post;
  $image = get_post_meta($post->ID, 'thesis_post_image');
  if ($image)
    echo '<img src="http://www.example.com/wp/wp-content/themes/thesis/lib/scripts/thumb.php?src='.$image.'&w=140&h=140&zc=1&q=100"></a>';
 }
}
add_action('thesis_hook_before_post','feature_thumbs');