How to dynamically write text on a image using ASP.Net C#

I am showing images in "img" control and image name in "Label" control. My requirement is that if downloads the image then image name should be displayed on image. I am using the following code to write on the image and download. It is working fine but when i see the downloaded image. The image is corrupt. If i download the image without writing then the image is o.k. Please suggest me that what i should make changes in my following coding that the image will not corrupt after writing. The code is given below:

 protected void Download_Click(object sender, ImageClickEventArgs e)
    {
        string imgPath = hdnId.Value;
        string[] a = imgPath.Split(new string[] { "demoProject/" }, StringSplitOptions.None);
        string ik = a[1].Replace("%20", " ");
        string[] a1 = imgPath.Split(new string[] { "Gallery/" }, StringSplitOptions.None);
        string sh = a1[1];      

        FileInfo file = new FileInfo(Server.MapPath(ik));        
        if (file.Exists)
        {         
            // Coding for write Text on the Image
            Bitmap bitMapImage = new System.Drawing.Bitmap(Server.MapPath(ik));
            Graphics graphicImage = Graphics.FromImage(bitMapImage);
            graphicImage.SmoothingMode = SmoothingMode.AntiAlias;

            SolidBrush brush = new SolidBrush(Color.Red);
            graphicImage.DrawString(lblText.Text, new Font("Arial", 17, FontStyle.Bold), brush, new Point(100, 250));
            Response.ContentType = "image/jpeg";
            bitMapImage.Save(Response.OutputStream, ImageFormat.Jpeg);
            bitMapImage.Save(Server.MapPath("images/PGImages/") + sh);           
            graphicImage.Dispose();
            bitMapImage.Dispose();
            //This is the image where we are going to write the text on it.       
               string imgName = "images/PGImages/" + sh;
        
// Coding for download the image.

            Response.Clear();
            Response.ContentType = (Path.GetExtension(imgName));
            Response.AddHeader("Content-Disposition",string.Format("attachment;     filename = {0}",Path.GetFileName(imgName)));
            Response.AddHeader("Content-Length", file.Length.ToString("F0"));
            Response.TransmitFile(imgName);
            Response.End();
        }
        else
        {
            Response.Write("This file does not exist.");
        }
    }