static void Main(string[] args)
    {
        var handle = new IntPtr();
        string title;
        FindWindowTitleMatch("notepad", out handle, out title);
        var bmp = CaptureApplication(handle);
        bmp.Save(@"C:test.bmp",ImageFormat.Bmp);
        var bmpfromfile = (Bitmap) Image.FromFile(@"C:test.bmp");
        var bytefromfile = ImageToByte(bmpfromfile);
        var bytefromSS = ImageToByte(bmp);


        Console.WriteLine(ByteArrayCompare(bytefromfile, bytefromSS));
        //false
    }

    [DllImport("msvcrt.dll", CallingConvention = CallingConvention.Cdecl)]
    static extern int memcmp(byte[] b1, byte[] b2, long count);

    static bool ByteArrayCompare(byte[] b1, byte[] b2)
    {
        // Validate buffers are the same length.
        // This also ensures that the count does not exceed the length of either buffer.
        return b1.Length == b2.Length && memcmp(b1, b2, b1.Length) == 0;
    }

    public static byte[] ImageToByte(Image img)
    {
        ImageConverter converter = new ImageConverter();
        return (byte[])converter.ConvertTo(img, typeof(byte[]));
    }

    public static Bitmap CaptureApplication(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, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
        Graphics graphics = Graphics.FromImage(bmp);
        graphics.CopyFromScreen(rect.left, rect.top, 0, 0, new Size(width, height), CopyPixelOperation.SourceCopy);
        return bmp;
    }