How to output thumbnail url

For listing detail page (thumbnail of the main image):

<?php echo $Thumbnail->thumb($listing,0,array('return_src'=>true,'tn_mode'=>$introThumbnailMode,'dimensions'=>array($introThumbnailSize)));?>

For the category/search list pages:

<?php echo $Thumbnail->thumb($listing,0,array('return_src'=>true,'tn_mode'=>$this->Config->list_thumb_mode,'location'=>'list','dimensions'=>array($this->Config->list_image_resize)));?>

For the listings module:

<?php echo $Thumbnail->thumb($listing, 0, array('return_src'=>true,'tn_mode'=>$tn_mode,'location'=>'module'.$tn_width,'dimensions'=>array($tn_width)));?>