string fileName = @"E:\exe\pic-0.jpeg";
            string fileName1 = @"E:\exe\pic-1.jpeg";
            string resultFileName = @"E:\exe\result.jpeg";

            int sizeX = 1676*2;
            int sizeY = 951;

            Image image = Image.FromFile(fileName);
            Image image1 = Image.FromFile(fileName1);
            Bitmap bmp = new Bitmap(sizeX, sizeY);

            Graphics gr = Graphics.FromImage(bmp);
            gr.CompositingQuality = CompositingQuality.HighQuality;
            gr.InterpolationMode = InterpolationMode.HighQualityBicubic;

            gr.DrawImage(image, 0, 0, 1676, 951);
            gr.DrawImage(image1, 1676, 0, 1676, 951);

            gr.Flush();
            File.Delete(resultFileName);

            FileStream st = new FileStream(resultFileName, FileMode.Create);
            bmp.Save(st, image.RawFormat);
            st.Close();

            image.Dispose();
image1.Dispose()

// bmp.Save(st, image.RawFormat);
   bmp.Save(st, ImageFormat.Png);