这个C#类专门用于图片缩略图处理，除了可以将图片缩小成指定大小的缩略图外，还可以用于给图片打上图片水印，

using System;  using System.Drawing.Imaging;  using System.Collections;  using System.Drawing;  using System.IO;     namespace DotNet.Utilities  {      /// <summary>      /// 枚举,生成缩略图模式      /// </summary>      public enum ThumbnailMod : byte      {          /// <summary>          /// HW          /// </summary>          HW,          /// <summary>          /// W          /// </summary>          W,          /// <summary>          /// H          /// </summary>          H,          /// <summary>          /// Cut          /// </summary>          Cut      };         /// <summary>      /// 操作图片类, 生成缩略图,添加水印      /// </summary>      public static class PicDeal      {          private static Hashtable htmimes = new Hashtable();          internal static readonly string AllowExt = ".jpe|.jpeg|.jpg|.png|.tif|.tiff|.bmp";          #region 生成缩略图          /// <summary>          /// 生成缩略图          /// </summary>          /// <param name="originalImagePath"></param>          /// <param name="width"></param>          /// <param name="height"></param>          /// <param name="mode"></param>          /// <returns></returns>          public static bool MakeThumbnail(string originalImagePath, int width, int height, ThumbnailMod mode)          {              string thumbnailPath = originalImagePath.Substring(0, originalImagePath.LastIndexOf('.')) + "s.jpg";              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 ThumbnailMod.HW://指定高宽缩放（可能变形）                                     break;                  case ThumbnailMod.W://指定宽，高按比例                                         toheight = originalImage.Height * width / originalImage.Width;                      break;                  case ThumbnailMod.H://指定高，宽按比例                      towidth = originalImage.Width * height / originalImage.Height;                      break;                  case ThumbnailMod.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              Image bitmap = new Bitmap(towidth, toheight);                 //新建一个画板              Graphics g = 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 Rectangle(0, 0, towidth, toheight),                  new Rectangle(x, y, ow, oh),                  GraphicsUnit.Pixel);              bool isok = false;              try              {                  //以jpg格式保存缩略图                  bitmap.Save(thumbnailPath, ImageFormat.Jpeg);                  isok = true;              }              catch (Exception)              {                  thumbnailPath = originalImagePath;              }              finally              {                  originalImage.Dispose();                  bitmap.Dispose();                  g.Dispose();              }              return isok;          }          #endregion             #region 在图片上生成图片水印          ///// <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>          /// <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_sypf">水印图片路径</param>          public static void AddWaterPic(string Path, string Path_sypf)          {              try              {                  Image image = Image.FromFile(Path);                  Image copyImage = Image.FromFile(Path_sypf);                  Graphics g = 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 + ".temp");                  image.Dispose();                  System.IO.File.Delete(Path);                  File.Move(Path + ".temp", Path);              }              catch              { }          }          #endregion             /// <summary>          /// 公共方法          /// </summary>          private static void GetImgType()          {              htmimes[".jpe"] = "image/jpeg";              htmimes[".jpeg"] = "image/jpeg";              htmimes[".jpg"] = "image/jpeg";              htmimes[".png"] = "image/png";              htmimes[".tif"] = "image/tiff";              htmimes[".tiff"] = "image/tiff";              htmimes[".bmp"] = "image/bmp";          }                #region 返回新图片尺寸          /// <summary>          /// 返回新图片尺寸          /// </summary>          /// <param name="width">原始宽</param>          /// <param name="height">原始高</param>          /// <param name="maxWidth">新图片最大宽</param>          /// <param name="maxHeight">新图片最大高</param>          /// <returns></returns>          public static Size ResizeImage(int width, int height, int maxWidth, int maxHeight)          {              decimal MAX_WIDTH = (decimal)maxWidth;              decimal MAX_HEIGHT = (decimal)maxHeight;              decimal ASPECT_RATIO = MAX_WIDTH / MAX_HEIGHT;                 int newWidth, newHeight;                 decimal originalWidth = (decimal)width;              decimal originalHeight = (decimal)height;                 if (originalWidth > MAX_WIDTH || originalHeight > MAX_HEIGHT)              {                  decimal factor;                  // determine the largest factor                  if (originalWidth / originalHeight > ASPECT_RATIO)                  {                      factor = originalWidth / MAX_WIDTH;                      newWidth = Convert.ToInt32(originalWidth / factor);                      newHeight = Convert.ToInt32(originalHeight / factor);                  }                  else                  {                      factor = originalHeight / MAX_HEIGHT;                      newWidth = Convert.ToInt32(originalWidth / factor);                      newHeight = Convert.ToInt32(originalHeight / factor);                  }              }              else              {                  newWidth = width;                  newHeight = height;              }                 return new Size(newWidth, newHeight);             }          #endregion      }  }