.net

<style>
#imgPreview
{ 
filter: progidXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale);
width: 136px;
height: 134px;
margin-left: 1px;
} 
</style>

Script:
<script src="http://code.jquery.com/jquery-1.9.1.js"></script>
 <script>
        function PreviewImg(input) {
            if (input.files && input.files[0]) {
                var reader = new FileReader();

                reader.onload = function (e) {
                    $('#imgPreview').attr('src', e.target.result);
                }

                reader.readAsDataURL(input.files[0]);
            }
        }
</script>

HTML :
<asp:FileUpload ID="file" runat="server" size="20" Width="258px" 
          onchange="PreviewImg(this)"/>
          <img id="imgPreview" src="#"/>