javascript 鼠标拖动IMG的问题

var offset_x;
var offset_y;
function Milan_StartMove(oEvent,div_id)
{    var whichButton;
    if(document.all&&oEvent.button==1) whichButton=true;
    else { if(oEvent.button==0)whichButton=true;}
    if(whichButton)
    { 
        var oDiv=div_id;
        offset_x=parseInt(oEvent.clientX-oDiv.offsetLeft);
        offset_y=parseInt(oEvent.clientY-oDiv.offsetTop);
        document.documentElement.onmousemove=function(mEvent)
        {    
            var eEvent;
            if(document.all) eEvent=event;
            else{eEvent=mEvent;}
            var oDiv=div_id;
            var x=eEvent.clientX-offset_x;
            var y=eEvent.clientY-offset_y;
            oDiv.style.left=(x)+"px";
            oDiv.style.top=(y)+"px";
            var d_oDiv=document.getElementById("disable_"+oDiv.id);
        }
    }
}
function Milan_StopMove(oEvent){document.documentElement.onmousemove=null; }
function div_Close(o)
{var oDiv=o; oDiv.style.display="none";var d_oDiv=document.getElementById("disable_"+o.id);d_oDiv.style.display="none";}<div id="oDiv" style="position:absolute;width:100px;height:61px;border:0px solid silver;left:100px;top:100px;z-index:9999;">
<div id="move" onmousedown="Milan_StartMove(event,this.parentNode)" onmouseup="Milan_StopMove(event)" ondblclick="Open('http://www.baidu.com')"; 
style="cursor:move;width:100%;height:61px;">
测试</div></div>
我是这样写的,现在正常用,要是把文字换成图片就不行了,鼠标点击放开时还跟着走,为什么啊