Bitmap bmp = new Bitmap(pictureBox1.Width, pictureBox1.Height);
pictureBox1.DrawToBitmap(bmp, new Rectangle(0, 0, pictureBox1.Width, pictureBox1.Height));
bmp.Save("C:\\123.png", System.Drawing.Imaging.ImageFormat.Png);
pictureBox1.DrawToBitmap(bmp, new Rectangle(0, 0, pictureBox1.Width, pictureBox1.Height));
bmp.Save("C:\\123.png", System.Drawing.Imaging.ImageFormat.Png);