Код xaml

   Random rnd = new Random();

        string CorrectAnswer = "";

        public MainWindow()

        {

            InitializeComponent();

            GenerateCaptcha();

        }

        public void GenerateCaptcha()

        {

            CaptchaStackPanel.Children.Clear();

            CorrectAnswer = "";

            for (int i = 0; i < 4; i++)

            {

                TextBlock textblock = new TextBlock();

                textblock.FontSize = 26;

                textblock.TextDecorations = TextDecorations.Strikethrough;

                textblock.Margin = new Thickness(0, rnd.Next(-10, 10), 0, rnd.Next(-10, 10));

                string tempChar = GenerateRandomString();

                CorrectAnswer += tempChar;

                textblock.Text = tempChar;

                CaptchaStackPanel.Children.Add(textblock);

            }

        }

        public string GenerateRandomString()

        {

            const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

            char randomChars = chars[rnd.Next(chars.Length)];

            return randomChars.ToString();

        }

        private void Button_Click(object sender, RoutedEventArgs e)

        {

            if (AnswerBox.Text == CorrectAnswer)

            {

                MessageBox.Show("Ответ верный");

                UserWindow userWindow = new UserWindow(AnswerBox.Text);

                userWindow.Login("1");

                userWindow.Show();

                AnswerBox.Text = "";

            }

            else

            {

                MessageBox.Show("Ответ неверный");

                AnswerBox.Text = "";

                GenerateCaptcha();

            }

        }