WordPress – The Post Thumbnail Caption

function the_post_thumbnail_caption() {
  global $post;

  $thumb_id = get_post_thumbnail_id($post->id);

  $args = array(
	'post_type' => 'attachment',
	'post_status' => null,
	'post_parent' => $post->ID,
	'include'  => $thumb_id
	); 

   $thumbnail_image = get_posts($args);

   if ($thumbnail_image && isset($thumbnail_image[0])) {
     //show thumbnail title
     echo $thumbnail_image[0]->post_title; 

     //Uncomment to show the thumbnail caption
     //echo $thumbnail_image[0]->post_excerpt; 

     //Uncomment to show the thumbnail description
     //echo $thumbnail_image[0]->post_content; 

     //Uncomment to show the thumbnail alt field
     //$alt = get_post_meta($thumbnail_id, '_wp_attachment_image_alt', true);
     //if(count($alt)) echo $alt;
  }
}