透過 Graphics 中的 CopyFromScreen 即可達到複製螢幕功能！

全螢幕擷取到檔案：

            Bitmap myImage = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height);
            Graphics g = Graphics.FromImage(myImage);
            g.CopyFromScreen(new Point(0,0), new Point(0, 0), new Size(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height));
            IntPtr dc1 = g.GetHdc();
            g.ReleaseHdc(dc1);
            myImage.Save(@"c:\screen.jpg",System.Drawing.Imaging.ImageFormat.Jpeg);