图片在显示时加上水印

上代码：

            //图片类型
            Response.ContentType = "image/jpeg";
            //元图路径
            string filePath = Server.MapPath("ImgUpload/" + "9d82d158ccbf6c81db35544dbe3eb13533fa4010.jpg");
            //水印内容
            string addText = "localhost";

            System.Drawing.Image image = System.Drawing.Image.FromFile(filePath);

            Bitmap bitmap = new Bitmap(image.Width, image.Height);

            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap);
            g.DrawImage(image, 0, 0, image.Width, image.Height);
            
            //字体
            System.Drawing.Font f = new System.Drawing.Font("Arial Black", 30.0f, System.Drawing.FontStyle.Bold);
            
            //笔刷色值
            System.Drawing.Brush b = new System.Drawing.SolidBrush(System.Drawing.Color.Green);


            //将原图画在位图上
            g.DrawImage(image, new Point(0, 0));

            //将水印加在位图上
            g.DrawString(addText, f, b, new System.Drawing.PointF(50,50));

            //将位图输入到流
            bitmap.Save(Response.OutputStream, ImageFormat.Jpeg);

            g.Dispose();
            image.Dispose();
            bitmap.Dispose();