var
  OldWinProc: TWndMethod;

procedure TForm1.FormCreate(Sender: TObject);
begin
  OldWinProc := Image1.WindowProc;
  Image1.WindowProc := NewWindowProc;
end;

procedure TForm1.ChangeState;
begin
  Image1.Picture.Bitmap.Canvas.FillRect(Image1.ClientRect);
  if ToEnter then begin
    Label1.Caption := 'Enter';
    ImageList1.GetBitmap(0, Image1.Picture.Bitmap);
  end
  else begin
    Label1.Caption := 'Leave';
    ImageList1.GetBitmap(1, Image1.Picture.Bitmap);
  end;
  Image1.Invalidate;
end;

procedure TForm1.NewWindowProc(var Msg: TMessage);
begin
  // все для того, чтоб исключить беспрерывный вызов ChangeState!
  if (Msg.Msg = CM_MouseLeave) or (Msg.Msg = CM_MouseEnter) then begin
    if (not MouseLeave and (Msg.Msg = CM_MouseLeave))
      or (MouseLeave and (Msg.Msg = CM_MouseEnter)) then ChangeState(MouseLeave);
    MouseLeave := (Msg.Msg = CM_MouseLeave);
    Beep; // би-бип
  end;
  OldWinProc(Msg);
end;