$obj_title = $this->item['title'];
echo JComments::showComments($obj_id, 'com_rsgallery2', $obj_title);
Try to replace your two lines with the following code :
$item = rsgInstance::getItem();
echo JComments::showComments($item->id, 'com_rsgallery2', $item->title);
It works by me but my RSgallery version is very hacked and I didn't test the new SVN version.
Hope it'll help

Hi vistamedia,
i tried your hack but i am getting same comments on all pics , some how the itemid and title is not echoing any result ,
may be coz i am using the latest version of RSGallery2
any solutions for that!!!
thanks in advance
dee