PaperSize ps = new PaperSize();
        ps.RawKind = (int)PaperKind.DLEnvelope;
        ps.Width = 416;
        ps.Height = 832;

        PrintDocument pd = new PrintDocument();
        pd.DefaultPageSettings.Landscape = true;
        pd.PrinterSettings.DefaultPageSettings.PaperSize = ps;
        pd.PrintPage += printDoc_PrintPage;
        pd.Print();

        void printDoc_PrintPage(object sender, PrintPageEventArgs e)
        {
        Image img = Image.FromFile(_path_img);
        e.Graphics.DrawImageUnscaled(img, 0, 0);
        }