DIV里的图片垂直居中

<style>
#dvImg{
  width:240px;
  height:235px;
  line-height:250px;
  border:2px solid #ddd;
  background:#fff;
  overflow:hidden;
 margin-left:200px;
  text-align:center;
}
#dvImg  p{
  position:absolute; top:50%;padding:0;margin:1px; background-color:#FFFF00;
}
#dvImg  img{
  position:relative; top:-50%;left:-50%;
}
</style>
<div id="dvImg">
 <p> <img src="http://img1.qq.com/news/pics/9499/9499744.gif"  /> </p>
</div>