图片水印

public class WaterImgHandler:IHttpHandler
    {

        public bool IsReusable
        {
            get { return false; }
        }

        public void ProcessRequest(HttpContext context)
        {
                 // 指定水印图片
            string water_Url = "~/wImages/logo.gif";
            // 指定默认图片
            string default_Url = "~/wImages/error.jpg";
            // 创建图片对象，用于存放用户读取的图片
            System.Drawing.Image g;
            // 判断所请求的图片是否存在，存在就给图片加水印
            if (File.Exists(context.Request.PhysicalPath))
            {
                g = System.Drawing.Image.FromFile(context.Request.PhysicalPath);
                // 加载水印图片
                System.Drawing.Image waterImg = System.Drawing.Image.FromFile(context.Request.MapPath(water_Url));
                Graphics gh = Graphics.FromImage(g);
                gh.DrawImage(waterImg, new RectangleF(0, g.Height - waterImg.Height, 100, 20));

                // 加载水印字符串
                Font font = new System.Drawing.Font("Arial", 6, System.Drawing.FontStyle.Bold);
                gh.DrawString("abcdefg", font, Brushes.White, 2, 2);
                gh.Dispose();
                waterImg.Dispose();
            }
            else { 
                // 图片不存在，显示默认图片
                g = System.Drawing.Image.FromFile(context.Request.MapPath(default_Url));
            }
            context.Request.ContentType = "image/jpeg";
            g.Save(context.Response.OutputStream,System.Drawing.Imaging.ImageFormat.Jpeg);
            g.Dispose();
            context.Response.End();

        }
    }
        // 最后在配置文件Web.config中写
      <httpHandlers>
         <add verb="*" path="*.jpg" type="Picture.WaterImgHandler"/>
     </httpHandlers>