兼容IE、新版Chrome、Firefox，实现本地图片等比例缩放预览 .

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>    
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />    
<title>本地图片预览</title>    
<style type="text/css">
#preview{width:100px;height:100px;border:1px solid #000;overflow:hidden;}
#imghead {filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=image);}
</style>
<script type="text/javascript">
function previewImage(file)
{
  var MAXWIDTH  = 100;
  var MAXHEIGHT = 100;
  var div = document.getElementById('preview');
  if (file.files && file.files[0])
  {
   div.innerHTML = '<img id=imghead>';
   var img = document.getElementById('imghead');
   img.onload = function(){
     var rect = clacImgZoomParam(MAXWIDTH, MAXHEIGHT, img.offsetWidth, img.offsetHeight);
     img.width = rect.width;
     img.height = rect.height;
     img.style.marginLeft = rect.left+'px';
     img.style.marginTop = rect.top+'px';
   }
   var reader = new FileReader();
   reader.onload = function(evt){img.src = evt.target.result;}
   reader.readAsDataURL(file.files[0]);
  }
  else
  {
    var sFilter='filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale,src="';
    file.select();
    var src = document.selection.createRange().text;
    div.innerHTML = '<img id=imghead>';
    var img = document.getElementById('imghead');
    img.filters.item('DXImageTransform.Microsoft.AlphaImageLoader').src = src;
    var rect = clacImgZoomParam(MAXWIDTH, MAXHEIGHT, img.offsetWidth, img.offsetHeight);
    status =('rect:'+rect.top+','+rect.left+','+rect.width+','+rect.height);
    div.innerHTML = "<div id=divhead style='width:"+rect.width+"px;height:"+rect.height+"px;margin-top:"+rect.top+"px;margin-left:"+rect.left+"px;"+sFilter+src+"\"'></div>";
  }
}
function clacImgZoomParam( maxWidth, maxHeight, width, height ){
 var param = {top:0, left:0, width:width, height:height};
 if( width>maxWidth || height>maxHeight )
 {
  rateWidth = width / maxWidth;
  rateHeight = height / maxHeight;
  
  if( rateWidth > rateHeight )
  {
   param.width =  maxWidth;
   param.height = Math.round(height / rateWidth);
  }else
  {
   param.width = Math.round(width / rateHeight);
   param.height = maxHeight;
  }
 }
 
 param.left = Math.round((maxWidth - param.width) / 2);
 param.top = Math.round((maxHeight - param.height) / 2);
 return param;
}
</script>    
</head>    
<body>
<div id="preview">
 <img id="imghead" width=100 height=100 border=0 src='../images/head01_big.jpg'>
</div>
    <br/>    
    <input type="file" onchange="previewImage(this)" />    
</body>    
</html>    

以上在IE6、IE7、IE8、Chrome 13.0.x、Firefox 10.0测试通过。IE9未作测试。