body{background:#3399CC}
#pngImg {
width: 300px;
height: 99px;
FILTER: Alpha(opacity=60);/*IE下半透明*/
-moz-opacity: 0.6;/*FF下半透明*/
}
</style>
<div id="pngImg"><img src="http://www.baidu.com/img/baidu_jgylogo1.gif" /></div>