为什么在IE8中不能浏览图片???????????

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="test1.aspx.cs" Inherits="web_admin_test1" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
    <title>get file input full path</title>    <script type="text/javascript" language='javascript'>
        function getFullPath(obj) {
            if (obj) {
                //ie 
                if (window.navigator.userAgent.indexOf("MSIE") >= 1) {
                    obj.select();                    return document.selection.createRange().text;
                }
                //firefox 
                else if (window.navigator.userAgent.indexOf("Firefox") >= 1) {
                    if (obj.files) {                        return obj.files.item(0).getAsDataURL();
                    }
                    return obj.value;
                }
                return obj.value;
            }
        }
    </script></head>
<body>
    <input type="file" onchange="document.getElementById('img').src=getFullPath(this);" />
    <img id="img" runat="server" alt="" src="" />
</body>
</html>
在火狐中可以浏览图片, 为什么在IE中就不能浏览了.口那位高手指点一下