procedure TForm1.FormCreate(Sender: TObject);
var
  i: integer;
  Image: TImage;
  Str: String;
  Jpeg: TJPegImage;
begin
  Application.ShowMainForm := False;
  Image := TImage.Create(Self);
  JPeg := TJPegImage.Create;
  try
    for i := 1 to ParamCount do
    begin
      Image.Picture.LoadFromFile(ParamStr(i));
      JPeg.Assign(Image.Picture.Graphic);
      JPeg.SaveToFile(ChangeFileExt(ParamStr(i), '.jpg'));
    end;
  finally
    Image.Free;
    JPeg.Free;
    Application.Terminate;
  end;
end;