一、原理及程序类型

　　原理：通过IE在本地打开目标URL同时截图；

　　本方法存在安全性的问题，千万不要为恶意网页生成缩略图，可能会给您带来一场灾难！

　　程序类型：C#语句(CS结构的程序)。

　　二、源代码

　　private void OnDocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
　　{
        WebBrowser browser = (sender as WebBrowser);
     
        if (browser != null)
        {
          mshtml.IHTMLDocument2 document = (browser.Document.DomDocument as mshtml.IHTMLDocument2);
          if (document != null)
          {
            mshtml.IHTMLElement element = (document.body as mshtml.IHTMLElement);
            if (element != null)
            {
              IHTMLElementRender render = (element as IHTMLElementRender);
              if (render != null)
              {
                using (Graphics graphics = this.CreateGraphics())
                {
                  IntPtr hdcDestination = graphics.GetHdc();
                  render.DrawToDC(hdcDestination);
                  IntPtr hdcMemory = GDI32.CreateCompatibleDC(hdcDestination);
                  IntPtr bitmap = GDI32.CreateCompatibleBitmap(
                    hdcDestination,
                    browser.ClientRectangle.Width,
                    browser.ClientRectangle.Height
                    );
               
                  if (bitmap != IntPtr.Zero)
                  {
                    IntPtr hOld = (IntPtr)GDI32.SelectObject(hdcMemory, bitmap);
                    GDI32.BitBlt(
                      hdcMemory,
                      0, 0,
                      browser.ClientRectangle.Width, browser.ClientRectangle.Height,
                      hdcDestination,
                      0, 0,
                      TernaryRasterOperations.SRCCOPY
                      );
                    GDI32.SelectObject(hdcMemory, hOld);
                    GDI32.DeleteDC(hdcMemory);
                    graphics.ReleaseHdc(hdcDestination);
                 
                    SaveThumbnail(Image.FromHbitmap(bitmap));
                  }
                }
              }
            }
          }
        }
　　}

　　通过以上代码获取URL页面的内容之后，使用如下代码可生成缩略图

　　private void SaveThumbnail(Image image)
　　{
        if (image != null)
        {//创建一个位图图像
          Bitmap thumbnail = new Bitmap(160, 120, PixelFormat.Format24bppRgb);
          thumbnail.SetResolution(image.HorizontalResolution, image.VerticalResolution);
       
          using (Graphics resize = Graphics.FromImage(thumbnail))
          {
            resize.InterpolationMode = InterpolationMode.HighQualityBicubic;
            resize.DrawImage(image,
              new Rectangle(0, 0, 160, 120),
              new Rectangle(0, 0, _webBrowser.ClientRectangle.Width, _webBrowser.ClientRectangle.Height),
              GraphicsUnit.Pixel);
          }
          thumbnail.Save(_file.FullName, ImageFormat.Png);
        }
　　}

　　经过测试并验证，效果不是很好，但是还能使用，足够使用拉！