CSS强制按比例缩小图片

<title>CSS强制按比例缩小图片</title>
<style>
img,a img{
border:0;
margin:0;
padding:0;
max-width:200px;
width:expression(this.width>200?"200px":this.width);
max-height:200px;
height:expression(this.height>200?"200px":this.height);
</style>
<img src="/jscss/demoimg/wall3.jpg">