AsyncFileUpload double upload

Hi, I trying to upload image using AsyncFileUpload and button. Below is the code I use to do it. But it causing double upload not sure how to let it upload image only after clicking the btnUpload. Current problem is that once I browse the image I want in asyncfileupload control there will be a loading.gif showing it loading and I refresh the page without clicking the btnUpload the image already been upload into database. What I wanted to do was let the image upload ONLY after clicking on the btnUpload. Do help out on solving this problem. THANKS!

Markup Code:

<script type="text/javascript" language="javascript">
        function StartUpload(sender, args) {
            var filename = args.get_fileName();
            var path = args.get_path();
            if (filename != "") {
                // code to get File Extension..
                var arr1 = new Array;
                arr1 = filename.split("\\");
                var len = arr1.length;
                var img1 = arr1[len - 1];
                var filext = img1.substring(img1.lastIndexOf(".") + 1);


                // Checking Extension
                if (filext == "jpg" || filext == "JPG") {
                    $get("<%=lblUpload.ClientID %>").innerHTML = "";
                    $get("<%=btnUpload.ClientID %>").disabled = false;
                    return true;
                }
                else {
                    $get("<%=lblUpload.ClientID %>").innerHTML = "Only .jpg and .JPG image allowed.";
                    $get("<%=btnUpload.ClientID %>").setAttribute('disabled', 'disabled');
                    return false;
                }
            }
        }</script>

<asp:AsyncFileUpload ID="AsyncFileUpload1" runat="server" 
CompleteBackColor="Lime" UploaderStyle="Modern" 
ErrorBackColor="Red" ThrobberID="Throbber" 
OnUploadedComplete="btnUpload_Click" 
UploadingBackColor="#66CCFF"
OnClientUploadStarted="StartUpload"
align="center"/>
<br /><br />
<asp:Label ID="Throbber" runat="server" Style="display: none"><img src="image/indicator.gif" alt="loading" /></asp:Label>
<asp:Button ID="btnUpload" runat="server" OnClick="btnUpload_Click" Text="Upload" />
<br /><br />
<asp:Label ID="lblUpload" runat="server" Text=""></asp:Label>

btnUpload Code:

protected void btnUpload_Click(object sender, EventArgs e)
        {
            if (AsyncFileUpload1.HasFile == true)
            {
                String nric = (String)Session["nric"];

                string filePath = AsyncFileUpload1.PostedFile.FileName;
                string filename = Path.GetFileName(filePath);
                string ext = Path.GetExtension(filename);

                string contenttype = String.Empty;

                switch (ext)
                {
                    case ".jpg":
                        contenttype = "image/jpg";
                        break;

                    case ".JPG":
                        contenttype = "image/jpg";
                        break;
                }
                if (contenttype != String.Empty)
                {
                    System.Drawing.Image uploaded = System.Drawing.Image.FromStream(AsyncFileUpload1.PostedFile.InputStream);

                    System.Drawing.Image newImage = new Bitmap(1024, 768);
                    using (Graphics g = Graphics.FromImage(newImage))
                    {
                        g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                        g.DrawImage(uploaded, 0, 0, 1024, 768);
                    }

                    byte[] results;
                    using (MemoryStream ms = new MemoryStream())
                    {
                        ImageCodecInfo codec = ImageCodecInfo.GetImageEncoders().FirstOrDefault(c => c.FormatID == ImageFormat.Jpeg.Guid);
                        EncoderParameters jpegParms = new EncoderParameters(1);
                        jpegParms.Param[0] = new EncoderParameter(Encoder.Quality, 95L);
                        newImage.Save(ms, codec, jpegParms);
                        results = ms.ToArray();
                    }

                    //insert the file into database
                    string strQuery = "Update MemberAccount Set profilepicture = @Data Where nric = @Nric";
                    SqlCommand cmd = new SqlCommand(strQuery);

                    cmd.Parameters.Add("@Nric", SqlDbType.VarChar).Value = nric;

                    cmd.Parameters.AddWithValue("@Data", results);

                    InsertUpdateData(cmd);

                    UpdatePanel2.Update();                    
                    
                    lblUpload.ForeColor = System.Drawing.Color.Green;
                    lblUpload.Text = "Profile Picture Updated.";
                }
            }
        }