窗口截圖，然後再使用Graphic類的方法剪裁

///
/// 提供全屏和指定窗口的截圖 以及保存爲文件的類
///
public class ScreenCapture
{
///
/// 全屏截圖
///
///
public Image CaptureScreen()
{
return CaptureWindow(User32.GetDesktopWindow());
}

        /// <summary>
        /// 指定窗口截圖
        /// </summary>
        /// <param name="handle">窗口句柄. (在windows應用程序中, 從Handle屬性獲得)</param>
        /// <returns></returns>
        public Image CaptureWindow(IntPtr handle)
        {
            IntPtr hdcSrc = User32.GetWindowDC(handle);
            User32.RECT windowRect = new User32.RECT();
            User32.GetWindowRect(handle, ref windowRect);
            int width = windowRect.right - windowRect.left;
            int height = windowRect.bottom - windowRect.top;
            IntPtr hdcDest = GDI32.CreateCompatibleDC(hdcSrc);
            IntPtr hBitmap = GDI32.CreateCompatibleBitmap(hdcSrc, width, height);
            IntPtr hOld = GDI32.SelectObject(hdcDest, hBitmap);
            GDI32.BitBlt(hdcDest, 0, 0, width, height, hdcSrc, 0, 0, GDI32.SRCCOPY);
            GDI32.SelectObject(hdcDest, hOld);
            GDI32.DeleteDC(hdcDest);
            User32.ReleaseDC(handle, hdcSrc);
            Image img = Image.FromHbitmap(hBitmap);
            GDI32.DeleteObject(hBitmap);
            return img;
        }

        /// <summary>
        /// 指定窗口截圖 保存爲圖片文件
        /// </summary>
        /// <param name="handle"></param>
        /// <param name="filename"></param>
        /// <param name="format"></param>
        public void CaptureWindowToFile(IntPtr handle, string filename, ImageFormat format)
        {
            Image img = CaptureWindow(handle);
            img.Save(filename, format);
        }

        /// <summary>
        /// 全屏截圖 保存爲文件
        /// </summary>
        /// <param name="filename"></param>
        /// <param name="format"></param>
        public void CaptureScreenToFile(string filename, ImageFormat format)
        {
            Image img = CaptureScreen();
            img.Save(filename, format);
        }

        /// <summary>
        /// 輔助類 定義 Gdi32 API 函數
        /// </summary>
        private class GDI32
        {

            public const int SRCCOPY = 0x00CC0020;
            [DllImport("gdi32.dll")]
            public static extern bool BitBlt(IntPtr hObject, int nXDest, int nYDest,
                int nWidth, int nHeight, IntPtr hObjectSource,
                int nXSrc, int nYSrc, int dwRop);
            [DllImport("gdi32.dll")]
            public static extern IntPtr CreateCompatibleBitmap(IntPtr hDC, int nWidth,
                int nHeight);
            [DllImport("gdi32.dll")]
            public static extern IntPtr CreateCompatibleDC(IntPtr hDC);
            [DllImport("gdi32.dll")]
            public static extern bool DeleteDC(IntPtr hDC);
            [DllImport("gdi32.dll")]
            public static extern bool DeleteObject(IntPtr hObject);
            [DllImport("gdi32.dll")]
            public static extern IntPtr SelectObject(IntPtr hDC, IntPtr hObject);
        }

        /// <summary>
        /// 輔助類 定義User32 API函數
        /// </summary>
        private class User32
        {
            [StructLayout(LayoutKind.Sequential)]
            public struct RECT
            {
                public int left;
                public int top;
                public int right;
                public int bottom;
            }
            [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("user32.dll")]
            public static extern IntPtr GetWindowRect(IntPtr hWnd, ref RECT rect);
        }
    }