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<?php

  function catch_that_image() {
    global $post, $posts;
    
    $first_img = '';
    ob_start();
    ob_end_clean();
    $output = preg_match_all( '/<img .+src=[\'"]([^\'"]+)[\'"].*/>/i', $post->post_content, $matches );
    $first_img = $matches [1] [0];
   
    if( empty( $first_img ) ) { //Defines a default image
      $first_img = '/images/default.jpg';
    }
    return $first_img;
  }

?>