Add multiple product images Magento

$newProduct = Mage::getModel(''catalog/product'')->load(productid)
$artworkhid = "image1.jpg,image2.jpg,image3.jpg";
$newProduct->setMediaGallery (array('images'=>array (), 'values'=>array ()));
$imgs = explode(',',$artworkhid);
 $i = 1;
foreach($imgs as $ims){
$previewImage = '/image_path/'.$ims;
     if(file_exists($previewImage)){
 if($i==1){
            $newProduct->addImageToMediaGallery ($previewImage, array ('thumbnail','small_image','image'), false, false);
      }else{
            $newProduct->addImageToMediaGallery ($previewImage, null, false, false);
  }
 $i++;
 }
}