怎么样通过Asp.net实现给图片添加水印？

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Collections;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
namespace ImageWriter
{
 /// <summary>
 /// 图片处理类
 /// </summary>
 public class ImageManager
 {
 #region 变量声明开始
 /// <summary>
 /// 枚举: 水印位置
 /// </summary>
 public enum WatermarkPosition
 {
 /// <summary>
 /// 左上
 /// </summary>
 LeftTop,
 /// <summary>
 /// 左中
 /// </summary>
 Left,
 /// <summary>
 /// 左下
 /// </summary>
 LeftBottom,
 /// <summary>
 /// 正上
 /// </summary>
 Top,
 /// <summary>
 /// 正中
 /// </summary>
 Center,
 /// <summary>
 /// 正下
 /// </summary>
 Bottom,
 /// <summary>
 /// 右上
 /// </summary>
 RightTop,
 /// <summary>
 /// 右中
 /// </summary>
 RightCenter,
 /// <summary>
 /// 右下
 /// </summary>
 RigthBottom
 }
 #endregion 变量声明结束
 #region 构造函数开始
 /// <summary>
 /// 构造函数: 默认
 /// </summary>
 public ImageManager()
 { }
 #endregion 构造函数结束
 #region 私有函数开始
 /// <summary>
 /// 获取: 图片去扩展名(包含完整路径及其文件名)小写字符串
 /// </summary>
 /// <param name="path">图片路径(包含完整路径,文件名及其扩展名): string</param>
 /// <returns>返回: 图片去扩展名(包含完整路径及其文件名)小写字符串: string</returns>
 private string GetFileName(string path)
 {
 return path.Remove(path.LastIndexOf('.')).ToLower();
 }
 /// <summary>
 /// 获取: 图片以'.'开头的小写字符串扩展名
 /// </summary>
 /// <param name="path">图片路径(包含完整路径,文件名及其扩展名): string</param>
 /// <returns>返回: 图片以'.'开头的小写字符串扩展名: string</returns>
 private string GetExtension(string path)
 {
 return path.Remove(0, path.LastIndexOf('.')).ToLower();
 }
 /// <summary>
 /// 获取: 图片以 '.' 开头的小写字符串扩展名对应的 System.Drawing.Imaging.ImageFormat 对象
 /// </summary>
 /// <param name="format">以 '. '开头的小写字符串扩展名: string</param>
 /// <returns>返回: 图片以 '.' 开头的小写字符串扩展名对应的 System.Drawing.Imaging.ImageFormat 对象: System.Drawing.Imaging.ImageFormat</returns>
 private ImageFormat GetImageFormat(string format)
 {
 switch (format)
 {
 case ".bmp":
  return ImageFormat.Bmp;
 case ".emf":
  return ImageFormat.Emf;
 case ".exif":
  return ImageFormat.Exif;
 case ".gif":
  return ImageFormat.Gif;
 case ".ico":
  return ImageFormat.Icon;
 case ".png":
  return ImageFormat.Png;
 case ".tif":
  return ImageFormat.Tiff;
 case ".tiff":
  return ImageFormat.Tiff;
 case ".wmf":
  return ImageFormat.Wmf;
 default:
  return ImageFormat.Jpeg;
 }
 }
 /// <summary>
 /// 获取: 枚举 Uinatlex.ToolBox.ImageManager.WatermarkPosition 对应的 System.Drawing.Rectangle 对象
 /// </summary>
 /// <param name="positon">枚举 Uinatlex.ToolBox.ImageManager.WatermarkPosition: Uinatlex.ToolBox.ImageManager.WatermarkPosition</param>
 /// <param name="X">原图宽度: int</param>
 /// <param name="Y">原图高度: int</param>
 /// <param name="x">水印宽度: int</param>
 /// <param name="y">水印高度: int</param>
 /// <param name="i">边距: int</param>
 /// <returns>返回: 枚举 Uinatlex.ToolBox.ImageManager.WatermarkPosition 对应的 System.Drawing.Rectangle 对象: System.Drawing.Rectangle</returns>
 private Rectangle GetWatermarkRectangle(WatermarkPosition positon, int X, int Y, int x, int y, int i)
 {
 switch (positon)
 {
 case WatermarkPosition.LeftTop:
  return new Rectangle(i, i, x, y);
 case WatermarkPosition.Left:
  return new Rectangle(i, (Y - y) / 2, x, y);
 case WatermarkPosition.LeftBottom:
  return new Rectangle(i, Y - y - i, x, y);
 case WatermarkPosition.Top:
  return new Rectangle((X - x) / 2, i, x, y);
 case WatermarkPosition.Center:
  return new Rectangle((X - x) / 2, (Y - y) / 2, x, y);
 case WatermarkPosition.Bottom:
  return new Rectangle((X - x) / 2, Y - y - i, x, y);
 case WatermarkPosition.RightTop:
  return new Rectangle(X - x - i, i, x, y);
 case WatermarkPosition.RightCenter:
  return new Rectangle(X - x - i, (Y - y) / 2, x, y);
 default:
  return new Rectangle(X - x - i, Y - y - i, x, y);
 }
 }
 #endregion 私有函数结束
 #region 文字生成开始
 #endregion 文字生成结束
 #region 设置透明度开始
 /// <summary>
 /// 设置: 图片 System.Drawing.Bitmap 对象透明度
 /// </summary>
 /// <param name="sBitmap">图片 System.Drawing.Bitmap 对象: System.Drawing.Bitmap</param>
 /// <param name="transparence">水印透明度(值越高透明度越低,范围在0.0f~1.0f之间): float</param>
 /// <returns>图片 System.Drawing.Bitmap: System.Drawing.Bitmap</returns>
 public Bitmap SetTransparence(Bitmap bm, float transparence)
 {
 if (transparence == 0.0f || transparence == 1.0f)
 throw new ArgumentException("透明度值只能在0.0f~1.0f之间");
 float[][] floatArray = 
 {
 new float[] { 1.0f, 0.0f, 0.0f, 0.0f, 0.0f }, 
 new float[] { 0.0f, 1.0f, 0.0f, 0.0f, 0.0f }, 
 new float[] { 0.0f, 0.0f, 1.0f, 0.0f, 0.0f }, 
 new float[] { 0.0f, 0.0f, 0.0f, transparence, 0.0f },
 new float[] { 0.0f, 0.0f, 0.0f, 0.0f, 1.0f } 
 };
 ImageAttributes imageAttributes = new ImageAttributes();
 imageAttributes.SetColorMatrix(new ColorMatrix(floatArray), ColorMatrixFlag.Default, ColorAdjustType.Bitmap);
 Bitmap bitmap = new Bitmap(bm.Width, bm.Height);
 Graphics graphics = Graphics.FromImage(bitmap);
 graphics.DrawImage(bm, new Rectangle(0, 0, bm.Width, bm.Height), 0, 0, bm.Width, bm.Height, GraphicsUnit.Pixel, imageAttributes);
 graphics.Dispose();
 imageAttributes.Dispose();
 bm.Dispose();
 return bitmap;
 }
 /// <summary>
 /// 设置: 图片 System.Drawing.Bitmap 对象透明度
 /// </summary>
 /// <param name="readpath">图片路径(包含完整路径,文件名及其扩展名): string</param>
 /// <param name="transparence">水印透明度(值越高透明度越低,范围在0.0f~1.0f之间): float</param>
 /// <returns>图片 System.Drawing.Bitmap: System.Drawing.Bitmap</returns>
 public Bitmap SetTransparence(string readpath, float transparence)
 {
 return SetTransparence(new Bitmap(readpath), transparence);
 }
 #endregion 设置透明度结束
 #region 添加水印开始
 /// <summary>
 /// 生成: 原图绘制水印的 System.Drawing.Bitmap 对象
 /// </summary>
 /// <param name="sBitmap">原图 System.Drawing.Bitmap 对象: System.Drawing.Bitmap</param>
 /// <param name="wBitmap">水印 System.Drawing.Bitmap 对象: System.Drawing.Bitmap</param>
 /// <param name="position">枚举 Uinatlex.ToolBox.ImageManager.WatermarkPosition : Uinatlex.ToolBox.ImageManager.WatermarkPosition</param>
 /// <param name="margin">水印边距: int</param>
 /// <returns>返回: 原图绘制水印的 System.Drawing.Bitmap 对象 System.Drawing.Bitmap</returns>
 public Bitmap CreateWatermark(Bitmap sBitmap, Bitmap wBitmap, WatermarkPosition position, int margin)
 {
 Graphics graphics = Graphics.FromImage(sBitmap);
 graphics.DrawImage(wBitmap, GetWatermarkRectangle(position, sBitmap.Width, sBitmap.Height, wBitmap.Width, wBitmap.Height, margin));
 graphics.Dispose();
 wBitmap.Dispose();
 return sBitmap;
 }
 #endregion 添加水印结束
 #region 图片切割开始
 #endregion 图片切割结束
 #region 图片缩放开始
 #endregion 图片缩放结束
 #region 保存图片到文件开始
 #region 普通保存开始
 /// <summary>
 /// 保存: System.Drawing.Bitmap 对象到图片文件
 /// </summary>
 /// <param name="bitmap">System.Drawing.Bitmap 对象: System.Drawing.Bitmap</param>
 /// <param name="writepath">保存路径(包含完整路径,文件名及其扩展名): string</param>
 public void Save(Bitmap bitmap, string writepath)
 {
 try
 {
 bitmap.Save(writepath, GetImageFormat(GetExtension(writepath)));
 bitmap.Dispose();
 }
 catch
 {
 throw new ArgumentException("图片保存错误");
 }
 }
 /// <summary>
 /// 保存: 对象到图片文件
 /// </summary>
 /// <param name="readpath">原图路径(包含完整路径,文件名及其扩展名): string</param>
 /// <param name="writepath">保存路径(包含完整路径,文件名及其扩展名): string</param>
 public void Save(string readpath, string writepath)
 {
 if (string.Compare(readpath, writepath) == 0)
 throw new ArgumentException("源图片与目标图片地址相同");
 try
 {
 Save(new Bitmap(readpath), writepath);
 }
 catch
 {
 throw new ArgumentException("图片读取错误");
 }
 }
 #endregion 普通保存结束
 #region 文字绘图保存开始
 #endregion 文字绘图保存结束
 #region 透明度调整保存开始
 /// <summary>
 /// 保存: 设置透明度的对象到图片文件
 /// </summary>
 /// <param name="sBitmap">图片 System.Drawing.Bitmap 对象: System.Drawing.Bitmap</param>
 /// <param name="transparence">水印透明度(值越高透明度越低,范围在0.0f~1.0f之间): float</param>
 /// <param name="writepath">保存路径(包含完整路径,文件名及其扩展名): string</param>
 public void SaveTransparence(Bitmap bitmap, float transparence, string writepath)
 {
 Save(SetTransparence(bitmap, transparence), writepath);
 }
 /// <summary>
 /// 保存: 设置透明度的象到图片文件
 /// </summary>
 /// <param name="readpath">原图路径(包含完整路径,文件名及其扩展名): string</param>
 /// <param name="transparence">水印透明度(值越高透明度越低,范围在0.0f~1.0f之间): float</param>
 /// <param name="writepath">保存路径(包含完整路径,文件名及其扩展名): string</param>
 public void SaveTransparence(string readpath, float transparence, string writepath)
 {
 Save(SetTransparence(readpath, transparence), writepath);
 }
 #endregion 透明度调整保存结束
 #region 水印图片保存开始
 /// <summary>
 /// 保存: 绘制水印的对象到图片文件
 /// </summary>
 /// <param name="sBitmap">原图 System.Drawing.Bitmap 对象: System.Drawing.Bitmap</param>
 /// <param name="wBitmap">水印 System.Drawing.Bitmap 对象: System.Drawing.Bitmap</param>
 /// <param name="position">枚举 Uinatlex.ToolBox.ImageManager.WatermarkPosition : Uinatlex.ToolBox.ImageManager.WatermarkPosition</param>
 /// <param name="margin">水印边距: int</param>
 /// <param name="writepath">保存路径(包含完整路径,文件名及其扩展名): string</param>
 public void SaveWatermark(Bitmap sBitmap, Bitmap wBitmap, WatermarkPosition position, int margin, string writepath)
 {
 Save(CreateWatermark(sBitmap, wBitmap, position, margin), writepath);
 }
 /// <summary>
 /// 保存: 绘制水印的对象到图片文件
 /// </summary>
 /// <param name="readpath">图片路径(包含完整路径,文件名及其扩展名): string</param>
 /// <param name="watermarkpath">水印图片路径(包含完整路径,文件名及其扩展名): string</param>
 /// <param name="transparence">水印透明度(值越高透明度越低,范围在0.0f~1.0f之间): float</param>
 /// <param name="position">枚举 Uinatlex.ToolBox.ImageManager.WatermarkPosition : Uinatlex.ToolBox.ImageManager.WatermarkPosition</param>
 /// <param name="margin">水印边距: int</param>
 /// <param name="writepath">保存路径(包含完整路径,文件名及其扩展名): string</param>
 public void SaveWatermark(string readpath, string watermarkpath, float transparence, WatermarkPosition position, int margin, string writepath)
 {
 if (string.Compare(readpath, writepath) == 0)
 throw new ArgumentException("源图片与目标图片地址相同");
 if (transparence == 0.0f)
 Save(readpath, writepath);
 else if (transparence == 1.0f)
 SaveWatermark(new Bitmap(readpath), new Bitmap(watermarkpath), position, margin, writepath);
 else
 SaveWatermark(new Bitmap(readpath), SetTransparence(watermarkpath, transparence), position, margin, writepath);
 }
 #endregion 水印图片保存结束
 #region 图片切割保存开始
 #endregion 图片切割保存结束
 #region 图片缩放保存开始
 #endregion 图片缩放保存开始
 #endregion 保存图片到文件结束
 }
}
/*
 调用很简单 im.SaveWatermark(原图地址, 水印地址, 透明度, 水印位置, 边距,保存位置); 
 Uinatlex.ToolBox.ImageManager im = new Uinatlex.ToolBox.ImageManager();
 im.SaveWatermark(Server.MapPath("/原图.jpg"), Server.MapPath("/水印.jpg"), 0.5f, Uinatlex.ToolBox.ImageManager.WatermarkPosition.RigthBottom, 10, Server.MapPath("/原图.jpg"));
 */

 protected void Page_Load(object sender, EventArgs e)
 {
 string newfileName = Server.MapPath("img/") + DateTime.Now.Millisecond + "" + DateTime.Now.Second + ".jpg";
 ImageManager im = new ImageManager();
 //调用很简单 im.SaveWatermark(原图地址, 水印地址, 透明度, 水印位置, 边距,保存到的位置); 
 im.SaveWatermark(Server.MapPath("img/Chrysanthemum.jpg"), Server.MapPath("img/woshi.jpg"), 0.9f, ImageManager.WatermarkPosition.RigthBottom, 10, newfileName);
 }