XHTML strict :)

There should be an alt an ending slash in image tag.

#164 - #168 should look like this:

     $path = variable_get('barcode_default_path', 'barcodes');
     if (!empty($element['#item']['title'])){
        return '<img src="/'.$filename.'" alt="'.$element['#item']['barcode'].'" /> -- '.$element['#item']['title'];
     }else return '<img src="/'.$filename.'" alt="'.$element['#item']['barcode'].'" />';
  }else return '';

OR

     $path = variable_get('barcode_default_path', 'barcodes');
     if (!empty($element['#item']['title'])){
        return '<img src="/'.$filename.'" alt="'.$element['#item']['title'] ? $element['#item']['title'] : $element['#item']['barcode'].'" /> -- '.$element['#item']['title'];
     }else return '<img src="/'.$filename.'" alt="'.$element['#item']['title'] ? $element['#item']['title'] : $element['#item']['barcode'].'" />';
  }else return '';