You first need to load the image form the database, then display it.
So something like that:
$db = JFactory::getDBO();
$db->setQuery('SELECT * FROM #__hikashop_file WHERE file_type=\'product\' AND file_ref_id='.$item->product_id);
$image = $db->loadObject();
$imageHelper = hikashop_get('helper.image');
$config =& hikashop_config();
$width = $config->get('thumbnail_x');
$height = $config->get('thumbnail_y');
$imageHelper->checkSize($width,$height,$image);
echo $imageHelper->display($image->file_path,true,$image->file_name,'style="margin-top:10px;margin-bottom:10px;display:inline-block;vertical-align:middle"', '', $width, $height);
You should add it in the loop displaying the product info.
For example, before the product name display code:
echo $item->order_product_name;