How to render webpage preview as thumbnail image

public static class NativeMethods
    {
        private const int SM_CXVSCROLL = 2;

        [ComImport]
        [Guid("0000010D-0000-0000-C000-000000000046")]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        private interface IViewObject
        {
            void Draw([MarshalAs(UnmanagedType.U4)] uint dwAspect, int lindex, IntPtr pvAspect, [In] IntPtr ptd, IntPtr hdcTargetDev, IntPtr hdcDraw, [MarshalAs(UnmanagedType.Struct)] ref Rect lprcBounds, [In] IntPtr lprcWBounds, IntPtr pfnContinue, [MarshalAs(UnmanagedType.U4)] uint dwContinue);
        }

        public static int GetSystemMetrics()
        {
            return GetSystemMetrics(SM_CXVSCROLL);
        }

        [DllImport("user32.dll")]
        public static extern int GetSystemMetrics(int smIndex);

        public static void GetImage(object obj, Image destination, Color backgroundColor)
        {
            using (var graphics = Graphics.FromImage(destination))
            {
                var deviceContextHandle = IntPtr.Zero;
                var rectangle =
                    new Rect
                    {
                        Right = destination.Width,
                        Bottom = destination.Height
                    };

                graphics.Clear(backgroundColor);
                try
                {
                    deviceContextHandle = graphics.GetHdc();

                    var viewObject = obj as IViewObject;
                    viewObject.Draw(1, -1, IntPtr.Zero, IntPtr.Zero, IntPtr.Zero, deviceContextHandle, ref rectangle, IntPtr.Zero, IntPtr.Zero, 0);
                }
                finally
                {
                    if (deviceContextHandle != IntPtr.Zero)
                    {
                        graphics.ReleaseHdc(deviceContextHandle);
                    }
                }
            }
        }
    }

public class HtmlToBitmapConverter : IDisposable
	{
		private const int SleepTimeMiliseconds = 5000;
//the output from the Render call
        internal static Bitmap Output;
		public Bitmap Render(string html, Size size)
		{
			var browser = CreateBrowser(size);
			browser.Navigate("about:blank");
			browser.Document.Write(html);
            Output = GetBitmapFromControl(browser, size);
			return Output;
		}
		public Bitmap Render(Uri uri, Size size)
		{
			var browser = CreateBrowser(size);            
			NavigateAndWaitForLoad(browser, uri, 0);
            Output = GetBitmapFromControl(browser, size);
            return Output;			
		}
		public void NavigateAndWaitForLoad(WebBrowser browser, Uri uri, int waitTime)
		{
			browser.Navigate(uri);
			var count = 0;
			while (browser.ReadyState != WebBrowserReadyState.Complete)
			{
				Thread.Sleep(SleepTimeMiliseconds);
				
				Application.DoEvents();
				count++;
				
				if (count > waitTime / SleepTimeMiliseconds)
				{
					break;
				}
			}
			while (browser.Document.Body == null)
			{
				Application.DoEvents();
			}
			HideScrollBars(browser);
		}
		private void HideScrollBars(WebBrowser browser)
		{
			const string Hidden = "hidden";
			var document = (IHTMLDocument2)browser.Document.DomDocument;
			var style = (IHTMLStyle2)document.body.style;
			style.overflowX = Hidden;
			style.overflowY = Hidden;            
		}
		private WebBrowser CreateBrowser(Size size)
		{
			var 
				newBrowser =
					new WebBrowser
					{
						ScrollBarsEnabled = false,
						ScriptErrorsSuppressed = true,
						Size = size
					};
			newBrowser.BringToFront();
			return newBrowser;
		}
		private Bitmap GetBitmapFromControl(WebBrowser browser, Size size)
		{
			var bitmap = new Bitmap(size.Width, size.Height);
			NativeMethods.GetImage(browser.Document.DomDocument, bitmap, Color.White);
			return bitmap;
		}
        void IDisposable.Dispose()
        {
            GC.SuppressFinalize(this);
        }
    }

[StructLayout(LayoutKind.Sequential, Pack = 4)]
    public struct Rect
    {
        public int Left;

        public int Top;

        public int Right;

        public int Bottom;
    }