All Monitor ScreenShot

public class ScreenCapture
{
    [DllImport("user32.dll")]
    public static extern IntPtr GetDesktopWindow();

    [DllImport("user32.dll")]
    public static extern IntPtr GetWindowDC(IntPtr hWnd);

    [DllImport("user32.dll")]
    public static extern IntPtr ReleaseDC(IntPtr hWnd, IntPtr hDC);

    [DllImport("gdi32.dll")]
    public static extern uint GetPixel(IntPtr hdc, int nXPos, int nYPos);

    public static Bitmap CaptureDesktop()
    {
        return CaptureWindow(GetDesktopWindow());
    }

    public static Bitmap CaptureWindow(IntPtr handle)
    {
        var rect = new User32.Rect();
        User32.GetWindowRect(handle, ref rect);

        int width = rect.right - rect.left;
        int height = rect.bottom - rect.top;

        var bmp = new Bitmap(width, height, PixelFormat.Format32bppArgb);
        Graphics graphics = Graphics.FromImage(bmp);
        graphics.CopyFromScreen(rect.left, rect.top, 0, 0, new Size(width, height), CopyPixelOperation.SourceCopy);

        return bmp;
    }
}