图片缩略图及水印

        /**/
        /// <summary>
        /// 生成缩略图
        /// </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)
        {
            System.Drawing.Image originalImage = System.Drawing.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（不变形）                
                    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;
                default:
                    break;
            }
            //新建一个bmp图片
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);
            //新建一个画板
            System.Drawing.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;
            //清空画布并以透明背景色填充
            g.Clear(System.Drawing.Color.Transparent);
            //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 System.Drawing.Rectangle(0, 0, towidth, toheight),
                new System.Drawing.Rectangle(x, y, ow, oh),
                System.Drawing.GraphicsUnit.Pixel);
            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();
            }
        }
        /**/
        /// <summary>
        /// 在图片上增加文字水印
        /// </summary>
        /// <param name="Path">原服务器图片路径</param>
        /// <param name="Path_sy">生成的带文字水印的图片路径</param>
        protected void AddWater(string Path, string Path_sy)
        {
            string addText = "中国";
            System.Drawing.Image image = System.Drawing.Image.FromFile(Path);
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(image);
            g.DrawImage(image, 0, 0, image.Width, image.Height);
            System.Drawing.Font f = new System.Drawing.Font("Verdana", 60);
            System.Drawing.Brush b = new System.Drawing.SolidBrush(System.Drawing.Color.Green);
            g.DrawString(addText, f, b, 35, 35);
            g.Dispose();
            image.Save(Path_sy);
            image.Dispose();
        }
        /**/
        /// <summary>
        /// 在图片上生成图片水印
        /// </summary>
        /// <param name="Path">原服务器图片路径</param>
        /// <param name="Path_syp">生成的带图片水印的图片路径</param>
        /// <param name="Path_sypf">水印图片路径</param>
        protected void AddWaterPic(string Path, string Path_syp, string Path_sypf)
        {
            System.Drawing.Image image = System.Drawing.Image.FromFile(Path);
            System.Drawing.Image copyImage = System.Drawing.Image.FromFile(Path_sypf);
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(image);
            g.DrawImage(copyImage, new System.Drawing.Rectangle(image.Width - copyImage.Width, image.Height - copyImage.Height, copyImage.Width, copyImage.Height), 0, 0, copyImage.Width, copyImage.Height, System.Drawing.GraphicsUnit.Pixel);
            g.Dispose();
            image.Save(Path_syp);
            image.Dispose();
        }

2种保存图片的方式

            //方式一
            var wreq = WebRequest.Create("http://zhigujin.com/Content/images/wjzm.png");
            var wresp = (HttpWebResponse)wreq.GetResponse();
            var s = wresp.GetResponseStream();
            var img = Image.FromStream(s);
            img.Save("D:\aa.gif", ImageFormat.Gif);
            //方式二
            var my = new WebClient();
            var mybyte  = my.DownloadData("http://files.jb51.net/file_images/article/201205/logo.gif");
            var ms = new MemoryStream(mybyte);
            Image img2 = Image.FromStream(ms);
            img2.Save("D:\a.gif", ImageFormat.Gif);   //保存