Delphi, inserting image in OpenOffice calc file

I need to insert images in "Calc" file using Open Office. The code from the answer to this question with minor changes works fine with Open Text documents so I decided to enhance it for Calc files but did not succeed - assigning Graphic.GraphicURL causes OLE error. How to fix it?

procedure InsertImage2;
var
  OleApp, Desktop, OpenParams, SaveParams, Document, Bitmaps, Sheet: Variant;
  SearchDescriptor, TextCursor, Graphic, Found: Variant;
  cb: integer;
  sSourceFile, sDestFile, sImageFile, sImageName, sLocationWord: string;
begin
  sSourceFile := 'file:///c:/test.ods';
  sDestFile := 'file:///c:/test2.ods';
  sImageFile := 'file:///c:/stamp.png';
  sImageName := 'Image1';
  sLocationWord := '[stamp]';
  OleApp := CreateOleObject('com.sun.star.ServiceManager');
  Desktop := OleApp.CreateInstance('com.sun.star.frame.Desktop');
  OpenParams := VarArrayCreate([0, -1], varVariant);
  Document := Desktop.LoadComponentFromURL(sSourceFile, '_blank', 0, OpenParams);
  Bitmaps := Document.CreateInstance('com.sun.star.drawing.BitmapTable');
  Bitmaps.insertByName(sImageName, sImageFile);
  if Document.supportsService('com.sun.star.sheet.SpreadsheetDocument') then
  begin
    for cb := 0 to Document.Sheets.Count - 1 do
    begin
      Sheet := Document.Sheets.getByIndex(cb);
      SearchDescriptor := Sheet.createSearchDescriptor;
      SearchDescriptor.setSearchString(sLocationWord);
      Found := Sheet.findFirst(SearchDescriptor);
      While not VarIsClear(Found) do
      begin
        TextCursor := Found.GetText.createTextCursor;
        TextCursor.gotoRange(Found, False);
        Graphic := Document.CreateInstance('com.sun.star.text.GraphicObject');
        Graphic.GraphicURL := Bitmaps.getByName(sImageName); //error "Variant does not reference an automation object"
        Graphic.AnchorType := 1;
        Graphic.Width := 6000;
        Graphic.Height := 6000;
        Found.GetText.insertTextContent(TextCursor, Graphic, True);
        Found := Sheet.findNext(Found.End, SearchDescriptor);
      end;
      SearchDescriptor := Unassigned;
      TextCursor := Unassigned;
      Found := Unassigned;
      Graphic := Unassigned;
    end;
    SaveParams := VarArrayCreate([0, -1], varVariant);
    Document.StoreAsURL(sDestFile, SaveParams);
  end;
  Document.Close(True);
  Bitmaps := Unassigned;
  OpenParams := Unassigned;
  SaveParams := Unassigned;
  Document := Unassigned;
end;