生成缩略图并添加水印

        /// <summary> 
        /// 生成缩略图 并加水印
         /// </summary> 
        /// <param name="originalImagePath">源图路径（物理路径）</param> 
        /// <param name="thumbnailPath">缩略图路径（物理路径）</param> 
        /// <param name="width">缩略图宽度</param> 
        /// <param name="height">缩略图高度</param> 
        /// <param name="mode">生成缩略图的方式</param> 
        public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)
{
            Image originalImage = Image.FromFile(originalImagePath);

            int towidth = width;
            int toheight = height;

            int x = 0;
            int y = 0;
            int ow = originalImage.Width;
            int oh = originalImage.Height;

            switch (mode)
            {
                case "HW"://指定高宽缩放（可能变形） 
                    break;
                case "W"://指定宽，高按比例 
                    toheight = originalImage.Height * width / originalImage.Width;
                    break;
                case "H"://指定高，宽按比例 
                    towidth = originalImage.Width * height / originalImage.Height;
                    break;
                case "Cut"://指定高宽裁减 
                    if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
                    {
                        oh = originalImage.Height;
                        ow = originalImage.Height * towidth / toheight;
                        y = 0;
                        x = (originalImage.Width - ow) / 2;
                    }
                    else
                    {
                        ow = originalImage.Width;
                        oh = originalImage.Width * height / towidth;
                        x = 0;
                        y = (originalImage.Height - oh) / 2;
                    }
                    break;
                case "CutA"://指定高宽裁减（不变形）自定义 
                    if (ow <= towidth && oh <= toheight)
                    {
                        x = -(towidth - ow) / 2;
                        y = -(toheight - oh) / 2;
                        ow = towidth;
                        oh = toheight;
                    }
                    else
                    {
                        if (ow > oh)//宽大于高 
                        {
                            x = 0;
                            y = -(ow - oh) / 2;
                            oh = ow;
                        }
                        else//高大于宽 
                        {
                            y = 0;
                            x = -(oh - ow) / 2;
                            ow = oh;
                        }
                    }
                    break;
                default:
                    break;
            }

            //新建一个bmp图片 
            Image bitmap = new System.Drawing.Bitmap(towidth, toheight);

            //新建一个画板 
            Graphics g = System.Drawing.Graphics.FromImage(bitmap);

            //设置高质量插值法 
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

            //设置高质量,低速度呈现平滑程度 
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

            //清空画布并以白色背景色填充 
            g.Clear(Color.White);

            //在指定位置并且按指定大小绘制原图片的指定部分 
            g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight),
            new Rectangle(x, y, ow, oh),
            GraphicsUnit.Pixel);


            //文字水印
            System.Drawing.Graphics testGrahpics = System.Drawing.Graphics.FromImage(bitmap);
            System.Drawing.Font font = new System.Drawing.Font("宋体", 14, System.Drawing.FontStyle.Bold);
            System.Drawing.Brush brush = new System.Drawing.SolidBrush(System.Drawing.Color.Gray);

            //分行
            string sInput = "Idgecn";    //获取输入的水印文字
            int coloum = 60;    //获取每行的字符数
            //利用循环，来依次输出
            for (int i = 0, j = 0; i < sInput.Length; i += coloum, j++)
            {
                //若要修改水印文字在照片上的位置，可将20修改成你想要的任何值
                if (j != sInput.Length / coloum)
                {
                    string s = sInput.Substring(i, coloum);
                    testGrahpics.DrawString(s, font, brush, 110, 10 * (i / coloum + 1));
                }
                else
                {
                    string s = sInput.Substring(i, sInput.Length % coloum);
                    testGrahpics.DrawString(s, font, brush, 110, 10 * (j + 1));

                }
            }

            testGrahpics.Dispose();
            try
            {
                //以jpg格式保存缩略图 
                bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
            }
            catch (System.Exception e)
            {
                throw e;
            }
            finally
            {
                originalImage.Dispose();
                bitmap.Dispose();
                g.Dispose();
            }
        }