//Use this to test it.
Rectangle rect = new Rectangle(0,0150,150);
Capture(rect);

public void Capture(Rectangle rect)
{
    var times = new List<long>();

    for (int i = 0; i < 100; i++)
    {
        using (Bitmap bmp = new Bitmap(rect.Width, rect.Height, PixelFormat.Format32bppArgb))
        {
            using (Graphics gdest = Graphics.FromImage(bmp))
            {
                using (Graphics gsrc = Graphics.FromHwnd(IntPtr.Zero))
                {

                    IntPtr hSrcDC = gsrc.GetHdc();
                    IntPtr hDC = gdest.GetHdc();

                    Stopwatch sw = new Stopwatch();

                    sw.Start();
                    int retval = BitBlt(hDC, 0, 0, rect.Width, rect.Height, hSrcDC, rect.Left, rect.Top, (int)CopyPixelOperation.SourceCopy);
                    sw.Stop();

                    gdest.ReleaseHdc();
                    gsrc.ReleaseHdc();

                    times.Add(sw.ElapsedMilliseconds);
                }
            }
        }
    }

    var mean = times.Sum(x => x) / times.Count;
    Console.WriteLine("Mean: " + mean);
}