asp.net中如何實現(xiàn)水印

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"; //水印圖片 
private const string DEFAULTIMAGE_URL = "~/Images/default.jpg";<span style="white-space:pre"> </span> //默認(rèn)圖片 
#region IHttpHandler 成員 
public bool IsReusable 
{ 
get { return false; } 
} 
public void ProcessRequest(HttpContext context) 
{ 
//context.Request.PhysicalPath //獲得用戶請求的文件物理路徑 
System.Drawing.Image Cover; 
//判斷請求的物理路徑中，是否存在文件 
if (File.Exists(context.Request.PhysicalPath)) 
{ 
//加載文件 
Cover = Image.FromFile(context.Request.PhysicalPath); 
//加載水印圖片 
Image watermark = Image.FromFile(context.Request.MapPath(WATERMARK_URL)); 
//通過書的封面得到繪圖對像 
Graphics g = Graphics.FromImage(Cover); 
//在image上繪制水印 
g.DrawImage(watermark, new Rectangle(Cover.Width - watermark.Width, Cover.Height - watermark.Height, 
 
 代碼如下:

watermark.Width, watermark.Height), 0, 0, watermark.Width, watermark.Height, GraphicsUnit.Pixel); 
//釋放畫布 
g.Dispose(); 
//釋放水印圖片 
watermark.Dispose(); 
} 
else 
{ 
//加載默認(rèn)圖片 
Cover = Image.FromFile(context.Request.MapPath(DEFAULTIMAGE_URL)); 
} 
//設(shè)置