水印图片

 public class CoverHandler : IHttpHandler
    {
        public bool IsReusable
        {
            get { return false; }
        }
        public CoverHandler() { }
        //水印图片路径
        private const string WATERMARK_URL = "~/images/button_nouse.gif";
        //默认图片路径
        private const string DEFAULTIMAGE_URL = "~/images/books_01.gif";
        public void ProcessRequest(HttpContext context)
        {
            //设置保存图片的类型
            context.Response.ContentType = "image/jpeg";
            //加载图片的路径
            string path = context.Request.MapPath(DEFAULTIMAGE_URL);
            //context.Request.PhysicalPath 为images/BookCovers下的图片
            if (File.Exists(context.Request.PhysicalPath))
            {
                //配置中存在路径就覆盖默认路径
                path = context.Request.PhysicalPath;
            }
            //加载图片路径
            using (Image Cover = Image.FromFile(path))
            {
                //加载水印图片路径
                using (Image watermark = Image.FromFile(context.Request.MapPath(WATERMARK_URL)))
                {
                   
                    if (path!=DEFAULTIMAGE_URL)
                    {
                        //实例化一个画布
                        using (Graphics g = Graphics.FromImage(Cover))
                        {
                            //添加水印到图片上
                            g.DrawImage(watermark, new Rectangle(Cover.Width- watermark.Width, Cover.Height- watermark.Height, watermark.Width, watermark.Height), 0, 0, watermark.Width, watermark.Height, GraphicsUnit.Pixel);
                        }
                    }
                   
                }
                //保存当前画布
                Cover.Save(context.Response.OutputStream,ImageFormat.Jpeg);
                //结束
                context.Response.End();
            }
        }
    }