In Internet Explorer 7 preview images are not shown

My code is working fine in Firefox and Internet Explorer 6 but Internet Explorer 7 is not showing images.

Here is the code,

<script type="text/javascript">
    function ShowImage()
    {
        //document.getElementById('videoupload').valuedocument.getElementById('videoupload').value.replace( "file:///", "")
        var img = document.createElement("IMG");
        if(document.all)
            img.src = document.getElemen开发者_运维技巧tById('videoupload').value;
        else if(window.sidebar)
        {
            //  solution for FF
            img.src = document.getElementById('videoupload').files.item(0).getAsDataURL();
        }
        else
            img.src = document.getElementById('videoupload').value;

        document.getElementById('show').appendChild(img);
        //alert(img.src);
    }
</script>
<form name="frmlist" enctype="multipart/form-data" method="post">
      Filename: <INPUT type="file" id="videoupload">
      <INPUT type="button" id="btn_video" onClick="ShowImage();" value="Upload">
 </form>
 <div id="show"></div>

It is a security issue since IE7. It will only work from low security, e.g. people will need to add your site to trusted sites or load the page from harddisk