Crop and Split image into parts and then save parts of image in C# ASP.Net

I tried your link and I did Crop height and weight of image.

Nw I want to save both parts of images in folder. 

I write code for crop image is following-

protected void Button1_Click(object sender, EventArgs e)
        {
            // Get the inputs.
            int wid = int.Parse("800");
            int hgt = int.Parse("1000");
            Bitmap bm = new Bitmap(FileUpload1.PostedFile.InputStream); ;

            // Start splitting the Bitmap.
            string piece_name =
                Path.GetFileNameWithoutExtension("photos/img1");
            Bitmap piece = new Bitmap(wid, hgt);
            Rectangle dest_rect = new Rectangle(0, 0, wid, hgt);
            using (Graphics gr = Graphics.FromImage(piece))
            {
                int num_rows = bm.Height / hgt;
                int num_cols = bm.Width / wid;
                Rectangle source_rect = new Rectangle(0, 0, wid, hgt);
                for (int row = 0; row < num_rows; row++)
                {
                    source_rect.X = 0;
                    for (int col = 0; col < num_cols; col++)
                    {
                        // Copy the piece of the image.
                        gr.DrawImage(bm, dest_rect, source_rect, GraphicsUnit.Pixel);

                        // Save the piece.
                        string filename = piece_name +
                            row.ToString("00") +
                            col.ToString("00") + ".bmp";
                        piece.Save(filename, ImageFormat.Bmp);

                        // Move to the next column.
                        source_rect.X += wid;
                    }
                    source_rect.Y += hgt;
                }
                Literal1.Visible = true;
                int abc = (num_rows * num_cols);
                Literal1.Text = abc.ToString();
            }
        }