How to add alternative text to a Webbrowser image?

{ Alternative Text for a image of a TWebBrowser }

procedure TForm1.Button1Click(Sender: TObject);
var
  HTMLDocument2Ifc: IHTMLDocument2;
  HTMLSelectionObjectIfc: IHTMLSelectionObject;
  HTMLTxtRangeIfc: IHTMLTxtRange;
begin
  HTMLDocument2Ifc := WebBrowser1.Document as IHTMLDocument2;
  HTMLDocument2Ifc.execCommand('InsertImage', False, '');
  HTMLSelectionObjectIfc := HTMLDocument2Ifc.selection;
  if HTMLSelectionObjectIfc.type_ = 'Control' then HTMLSelectionObjectIfc.Clear;
  HTMLTxtRangeIfc := HTMLSelectionObjectIfc.createRange as IHTMLTxtRange;
  HTMLTxtRangeIfc.pasteHTML('<image alt="Hello" src="c:\test.gif"> ');
end;