Capture All Monitors

gistfile1.cs

 [STAThread]
        static void Main()
        {
            var size = Screen.AllScreens.Aggregate(Size.Empty, (sz, screen) =>
            {
                var boundHeight = screen.Bounds.Y + screen.Bounds.Height;
                var boundWidth = screen.Bounds.X + screen.Bounds.Width;
                return new Size(boundWidth > sz.Width? boundWidth : sz.Width, boundHeight > sz.Height? boundHeight : sz.Height);
            });
            using (var bitmap = new Bitmap(size.Width, size.Height))
            {
                using (var graphics = Graphics.FromImage(bitmap))
                {
                    foreach (var screen in Screen.AllScreens)
                    {
                        graphics.CopyFromScreen(screen.Bounds.Location, screen.Bounds.Location, screen.Bounds.Size);
                    }
                }
                using (var fileStream = new FileStream("C:\\foo.png", FileMode.Create))
                {
                    bitmap.Save(fileStream, ImageFormat.Png);
                }
            }
        }

Need a reference to System.Windows.Forms and System.Drawing.