{ Increase the default undo limit }
ImageEnView1.Proc.UndoLimit := 99;
{ Do not automatically call TImageEnProc.SaveUndo }
ImageEnView1.Proc.AutoUndo := False;

procedure TForm1.ImageEnView1KeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
  if (Key = VK_DELETE) and (ImageEnView1.LayersCurrent <> 0) then
  begin
    ImageEnView1.Proc.SaveUndo('Delete layer', ieuLayer, True);
    ImageEnView1.LayersRemove(ImageEnView1.LayersCurrent);
    UpdateUndoMenu;
    UpdateGUI;
    UpdateStatusBar;
  end;
end;

procedure TForm1.Undo1Click(Sender: TObject);
 { Undo the last change }
begin
  if Assigned(ImageEnView1.IEBitmap) then
  begin
    with ImageEnView1 do
    begin
      with Proc do
      begin
        Undo;
        ClearUndo;
      end;
      IO.Params.Width := ImageEnView1.IEBitmap.Width;
      IO.Params.Height := ImageEnView1.IEBitmap.Height;
      Update;
      IEBitmap.Modified := Proc.CanUndo;
    end;
    UpdateUndoMenu;
    UpdateStatusBar;
  end;
end;