// This byte knows which icon is currently displayed
 const
   CurrentState : byte = 1;
   
 procedure TForm1.Timer1Timer(Sender: TObject);
 begin
   if IsIconic(Application.Handle) then
   begin
    case CurrentState of
    1: Application.Icon := Image1.Picture.Icon;
    2: Application.Icon := Image2.Picture.Icon;
    3: Application.Icon := Image3.Picture.Icon;
    4: Application.Icon := Image4.Picture.Icon;
    end; { case }
    InvalidateRect(Application.Handle, nil, True); // critical!
    if CurrentState >= 4 then
      CurrentState := 1
 	else
      inc(CurrentState);	 
   end;
 end;