/**//// <summary>
        /// 功能：将文字写入图片
        /// 日期：2006-11-20
        /// 作者：杨义贤
        /// </summary>
        /// <param name="strfileName">文件名字</param>
        /// <param name="strtext">需要写入的文字</param>
        private void TextToImage(string strfileName,string strtext)
        {
            if(!File.Exists(MapPath(strfileName)))
            {
                throw new FileNotFoundException("文件不存在!");
            }
          
            if( strtext == string.Empty )
            {
                return;
            }
            //还需要判断文件类型是否为图像类型
            System.Drawing.Image image = System.Drawing.Image.FromFile(MapPath(strfileName));
            Bitmap bitmap = new Bitmap(image,image.Width,image.Height);
            Graphics grap = Graphics.FromImage(bitmap);
            float fontSize = 24.0f;             //字体大小
            float textWidth = strtext.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 rectX = 0;      
            float rectY = 0;
            float rectWidth = strtext.Length*(fontSize+12);
            float rectHeight = fontSize+8;
            string strFont;//定义字体类型
            //声明矩形域
            RectangleF textArea = new RectangleF(rectX,rectY,rectWidth,rectHeight);
            strFont = ddlfont.SelectedItem.Text.ToString().Trim();
            Font font = new Font(strFont,fontSize);   //定义字体
            Brush whiteBrush = new SolidBrush(Color.White);   //白笔刷，画文字用
            Brush blackBrush = new SolidBrush(Color.Transparent);   //黑笔刷，画背景用

            grap.FillRectangle(blackBrush,rectX,rectY,rectWidth,rectHeight);          

            grap.