jqthumb.js缩略图插件-让缩略图正常显示而不变形

<script src="js/jqthumb.js"></script>

<script>
$(function(){
	$('.element2 img').jqthumb({
		width:260,
		height:170,
		after: function(imgObj){
			imgObj.css('opacity', 0).animate({opacity: 1}, 2000);
		}
	});
});
</script>

<ul class="element">
	<li class="element1"><img src="images/1.jpg" alt=""></li>
	<li class="element2"><img src="images/1.jpg" alt=""></li>
</ul>