<script>
function readURL(input) {
if (input.files && input.files[0]) {
var reader = new FileReader();
reader.onload = function(e) {
$('#blah').attr('src', e.target.result);
}
reader.readAsDataURL(input.files[0]);
}
}
$("#filePhoto").change(function() {
readURL(this);
});
</script>
<div>
<asp:FileUpload ID="FilePhoto" runat="server" CssClass="fileupload" onchange="readURL(this)" /><br />
<img id="blah" src="#" alt="Preview" width="100" height="100" />
</div>