public Bitmap CaptureFromScreen(Rectangle rect)
    {
        Bitmap bmpScreenCapture = null;

        if (rect == Rectangle.Empty)//capture the whole screen
        {
            bmpScreenCapture = new Bitmap(Screen.PrimaryScreen.Bounds.Width,
            Screen.PrimaryScreen.Bounds.Height);
        }
        else // just the rect
        {
            bmpScreenCapture = new Bitmap(rect.Width,rect.Height);
        }

        Graphics p = Graphics.FromImage(bmpScreenCapture);

        if (rect == Rectangle.Empty)
        { // captuer the whole screen
            p.CopyFromScreen(Screen.PrimaryScreen.Bounds.X,
                                     Screen.PrimaryScreen.Bounds.Y,
                                     0, 0,
                                     bmpScreenCapture.Size,
                                     CopyPixelOperation.SourceCopy);

        }
        else // cut a spacific rectangle
        {
            p.CopyFromScreen(rect.X,
                     rect.Y,
                     0, 0,
                     rect.Size,
                     CopyPixelOperation.SourceCopy);

        }

        return bmpScreenCapture;
    }

public Color GetColorFromScreen(Point p)
    {
        Rectangle rect = new Rectangle(p, new Size(2, 2));

        Bitmap map = CaptureFromScreen(rect);

        Color c = map.GetPixel(0, 0);

        map.Dispose();

        return c;
    }