一个回调问题，求高手！！

Question

       protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
               AddTextToImg("./images/home1.jpg",0);
            }
        }
            private void AddTextToImg(string fileName,int count)
        {
            if (!File.Exists(MapPath(fileName)))
            {
                throw new FileNotFoundException("The file don't exist!");
            }            System.Drawing.Image image = System.Drawing.Image.FromFile(MapPath(fileName));
            Bitmap bitmap = new Bitmap(image, image.Width, image.Height);
            Graphics g = Graphics.FromImage(bitmap);
     
            string strsql = "select categoryName from old_Category";
            string strwhere = "pid=1";
            float rectY = 192f;
            DataSet ds = Dbhelper.SQLHelper.GetDataSetWhere(strsql, strwhere);
            for (int i = count + 1; i <= ds.Tables[0].Rows.Count; i = ++)//count + 1
            {
                string text = ds.Tables[0].Rows[i-1]["categoryName"].ToString();
                float fontSize = 20.0f;    //字体大小   
                float textWidth = text.Length * fontSize;  //文本的长度   
                //下面定义一个矩形区域，以后在这个矩形里画上白底黑字   
                float rectWidth = text.Length * (fontSize + 8);
                float rectHeight = fontSize + 8;
                RectangleF textArea = new RectangleF(140, rectY, 360, 230);//声明矩形域 
                Font font = new Font("黑体", fontSize);//定义字体 
                Brush whiteBrush = new SolidBrush(Color.Black);//黑笔刷，画背景用   
                g.DrawString(text, font, whiteBrush, textArea);  
                rectY += 60;
                if (i % 4 == 0)
                {
                    int a = i / 4;
                    bitmap.Save("F:\\"+a+".jpg", ImageFormat.Jpeg);
                    g.Dispose();
                    bitmap.Dispose();
                    image.Dispose();
                    rectY = 192f;
                    AddTextToImg("./images/home1.jpg",a*4);
                }
            }            //MemoryStream ms = new MemoryStream();
            //保存为Jpg类型   
            int end = (Convert.ToInt32(ds.Tables[0].Rows.Count) / 4) + 1;
            bitmap.Save("F:\\"+end+".jpg", ImageFormat.Jpeg);            //输出处理后的图像，这里为了演示方便，我将图片显示在页面中了   
            Response.Clear();
            Response.ContentType = "image/jpeg";
            //Response.BinaryWrite(ms.ToArray());            g.Dispose();
            bitmap.Dispose();
            image.Dispose();
        }