C#

using Microsoft.WindowsAPICodePack.Taskbar;
private TabbedThumbnail customThumbnail;
protected override void OnShown(EventArgs e)
		{
			base.OnShown(e);

			customThumbnail = new TabbedThumbnail(this.Handle, this.Handle);
			TaskbarManager.Instance.TabbedThumbnail.AddThumbnailPreview(customThumbnail);
			customThumbnail.TabbedThumbnailBitmapRequested += customThumbnail_TabbedThumbnailBitmapRequested;
        }

		private Bitmap GenerateBitmap()
		{
			Bitmap bitmap = new Bitmap(150, 150);

			using (var g = Graphics.FromImage(bitmap))
			{
                g.DrawImage(Properties.Resources.tx, new Rectangle(0,0,150,150));
			}

			return bitmap;
		}
		void customThumbnail_TabbedThumbnailBitmapRequested(object sender, TabbedThumbnailBitmapRequestedEventArgs e)
		{
			var bitmap = GenerateBitmap();
			customThumbnail.SetImage(bitmap);

			ThreadPool.QueueUserWorkItem(c =>
			                             	{
			                             		Thread.Sleep(2000);
			                             		this.Invoke(new MethodInvoker(InvalidateThumbnail));
			                             	});
		}
		private void InvalidateThumbnail()
		{
			customThumbnail.InvalidatePreview();
		}

public class MyClass<T>
{
}

public enum WMessages : int
        {
            WM_MOUSEMOVE=                    0x0200,

            WM_LBUTTONDOWN = 0x201,
            WM_LBUTTONUP = 0x202,
            WM_RBUTTONDOWN = 0x0204,
            WM_RBUTTONUP = 0x0205,

            WM_KEYDOWN = 0x100,
            WM_KEYUP = 0x101,

            WH_KEYBOARD_LL = 13,
            WH_MOUSE_LL = 14,
        }
[DllImport("User32.Dll", EntryPoint = "PostMessageA")]
        static extern bool PostMessage(IntPtr hWnd, uint msg, int wParam, int lParam);
        private int MAKELPARAM(int p, int p_2)
        {
            return (p_2 * 0x10000 + p);
        }
        public void SendClick(WMessages type, Point pos, IntPtr hwnd)
        {
            switch (type)
            {
                case WMessages.WM_LBUTTONDOWN:
                    PostMessage(hwnd,
                        (int)0x201, 1,
                        MAKELPARAM(pos.X, pos.Y));//(IntPtr)((pos.Y << 16) | (pos.X & 0xFFFF)));
                    return;
                case WMessages.WM_LBUTTONUP:
                    PostMessage(hwnd,
                        (int)WMessages.WM_LBUTTONUP, 0, // <--(2) but you are telling to do WM_LBUTTONDOWN
                        MAKELPARAM(pos.X, pos.Y));//(IntPtr)((pos.Y << 16) | (pos.X & 0xFFFF)));
                    return;
                default:
                    return;
            }
        }

IntPtr atat = (IntPtr)0x00010870;
SendRClick(WMessages.WM_RBUTTONDOWN, new Point(50, 50), atat);
SendRClick(WMessages.WM_RBUTTONUP, new Point(50, 50), atat);