在网页里图片跑马灯效果怎么实现?

<div id="demob" align="center" onmouseover="ij=1" style="border:0px solid gray;OVERFLOW: hidden; HEIGHT: 570px; width:193px " onmouseout="ij=0">
<div id="demob1">

</div>
<div id="demob2"></div>
</div> <SCRIPT>
var ij=0;t=demob.scrollTop

demob2.innerHTML=demob1.innerHTML

function qswhMarquee2(){

if (ij==1)return

if(demob2.offsetTop-demob.scrollTop<=0)

demob.scrollTop-=demob1.offsetHeight

else

demob.scrollTop++

}

setInterval(qswhMarquee2,50)
</SCRIPT>

自己研究。懒得解释了