asp.net中水印的具体实现代码

using System;  
using System.Collections.Generic;  
using System.Linq;  
using System.Web;  
using System.Drawing;  
using System.IO;  

namespace BookShop.Web  
{  
    public class WaterMark : IHttpHandler  
    {  

        private const string WATERMARK_URL = "'/Images/watermark.jpg";        //水印图片  
        private const string DEFAULTIMAGE_URL = "'/Images/default.jpg";<span style="white-space:pre">   </span>      //默认图片  
        #region IHttpHandler 成员  

        public bool IsReusable  
        {  
            get { return false; }  
        }  

        public void ProcessRequest(HttpContext context)  
        {  

            //context.Request.PhysicalPath  //获得用户请求的文件物理路径  

            System.Drawing.Image Cover;  
            //判断请求的物理路径中，是否存在文件  
            if (File.Exists(context.Request.PhysicalPath))  
            {  
                //加载文件  
                Cover = Image.FromFile(context.Request.PhysicalPath);  
                //加载水印图片  
                Image watermark = Image.FromFile(context.Request.MapPath(WATERMARK_URL));  
            //通过书的封面得到绘图对像  
                Graphics g = Graphics.FromImage(Cover);  
                //在image上绘制水印  
                g.DrawImage(watermark, new Rectangle(Cover.Width - watermark.Width, Cover.Height - watermark.Height,   
[csharp] view plaincopy
watermark.Width, watermark.Height), 0, 0, watermark.Width, watermark.Height, GraphicsUnit.Pixel);  
                //释放画布  
                g.Dispose();  
                //释放水印图片  
                watermark.Dispose();  
            }  
            else 
            {  
                //加载默认图片  
                Cover = Image.FromFile(context.Request.MapPath(DEFAULTIMAGE_URL));  
            }  
            //设置输出格式  
            context.Response.ContentType = "image/jpeg";  
            //将图片存入输出流  
            Cover.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);  
            Cover.Dispose();  
            context.Response.End();  
        }  

        #endregion  
    }  
}