title: Get default post thumbnail from custom field
body: <p>This is default post thumbnail code</p>
  
  <pre><code>add_filter( 'post_thumbnail_html', 'my_post_thumbnail_html' );
  
  function my_post_thumbnail_html( $html ) 
  {
      if ( empty( $html ) )
          $html = '&lt;img src="' . trailingslashit( get_stylesheet_directory_uri() ) . 'images/default-thumbnail.png' . '" alt="" /&gt;';
  
      return $html;
  } 
  </code></pre>
  
  <p>I want to get post thumbnail with this from a custom field</p>
  
  <pre><code>/wp-content/plugins/postt/&lt;?php echo get_post_meta( get_the_ID(), 'img', true ); ?&gt;.jpg
  </code></pre>
  
  <p>How I can do it?</p>