太晚了，哈哈。今天有点神经，继续发表吧。
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<style>
div{
position:absolute;
}
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<body>
<div id="divImg">
<img src="http://a0.att.hudong.com/68/12/01300000012894119556127736723.jpg" width="130" height="180">
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//获取图片div对象
var img1=document.getElementById("divImg");
//设置div起始点的坐标(0,0）左上角坐标
var x=0,y=0;
//右下边求出图片起始点最大X和Y的坐标值
var w=window.screen.availWidth-130,h=window.screen.availHeight-180;
function floatimg(){
//随机产生坐标x和坐标Y的值（都是从零到起始点最大X和Y的坐标值）
x=Math.round(Math.random()*(w));
y=Math.round(Math.random()*(h));
//alert(x+","+y);
img1.style.left=x+"px";
img1.style.top=y+"px";
setTimeout("floatimg()",1000);
}
floatimg();
</script>
</body>
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