[C#] Captcha Generator

using System;
using System.Text;
using System.Drawing;
using System.Windows.Forms;
using System.Drawing.Drawing2D;

class CaptchaBox : PictureBox
{
    #region Properties
    private Color _textcolor = Color.Black;
    public Color TextColor
    {
        get { return _textcolor; }
        set { _textcolor = value; Invalidate(); }
    }

    private Font _font = new Font("Segoe UI", 20);
    public override Font Font
    {
        get { return _font; }
        set { _font = value; Invalidate(); }
    }

    private string _texttouse = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmopqrstuvwxyz!#$%^&*()1234567890";
    public string RandomCharacters
    {
        get { return _texttouse; }
        set { _texttouse = value; Invalidate(); }
    }

    private int _captchalength = 8;
    public int CaptchaTextLength
    {
        get { return _captchalength; }
        set { _captchalength = value; Invalidate(); }
    }

    private int _numberoflines = 50;
    public int NumberOfLines
    {
        get { return _numberoflines; }
        set { _numberoflines = value; Invalidate(); }
    }
    #endregion

    #region Events
    public CaptchaBox()
    {
        SetStyle(ControlStyles.AllPaintingInWmPaint, true);
        SetStyle(ControlStyles.ResizeRedraw, true);
        SetStyle(ControlStyles.UserPaint, true);
        SetStyle(ControlStyles.OptimizedDoubleBuffer, true);
        SetStyle(ControlStyles.SupportsTransparentBackColor, true);
    }

    protected override void CreateHandle()
    {
        base.CreateHandle();
        this.Size = new Size(241, 69);
        this.BorderStyle = BorderStyle.FixedSingle;
    }

    public string CaptchaText = string.Empty;
    private Random rnd = new Random();
    protected override void OnPaint(PaintEventArgs e)
    {
        Bitmap B = new Bitmap(Width, Height);
        Graphics G = Graphics.FromImage(B);

        Rectangle BoxSize = new Rectangle(0, 0, this.Width, this.Height);
        Brush txtcolor = new SolidBrush(Color.FromArgb(rnd.Next(160, 255), _textcolor));
        G.SmoothingMode = SmoothingMode.HighQuality;

        G.Clear(BackColor);

        for (int I = 0; I < _numberoflines; I++)
        {
            G.DrawLine(new Pen(Color.FromArgb(rnd.Next(128, 255),CreateRandomColor())), rnd.Next(0, BoxSize.Width), rnd.Next(0, BoxSize.Height), rnd.Next(BoxSize.Width), rnd.Next(BoxSize.Height));
        }

        StringFormat SFormat = new StringFormat();
        SFormat.Alignment = StringAlignment.Center;
        SFormat.LineAlignment = StringAlignment.Center;

        G.RotateTransform(rnd.Next(-7, 7), MatrixOrder.Append);

        string randomstr = CreateRandomString();
        G.DrawString(randomstr, Font, txtcolor, BoxSize, SFormat);
        CaptchaText = randomstr;

        e.Graphics.DrawImage(B, 0, 0);
        G.Dispose(); B.Dispose();
    }
    #endregion

    #region Create Randoms
    private Color CreateRandomColor()
    {
        return Color.FromArgb(100, rnd.Next(255), rnd.Next(255), rnd.Next(255));
    }

    private string CreateRandomString()
    {
        char[] buffer = new char[_captchalength];
        for (int i = 0; i < _captchalength; i++)
        {
            if (_texttouse == string.Empty)
            {
                string newtext = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmopqrstuvwxyz1234567890";
                buffer[i] = newtext[rnd.Next(newtext.Length)];
            }
            else
            {
                buffer[i] = _texttouse[rnd.Next(_texttouse.Length)];
            }
        }
        return new string(buffer);
    }
    #endregion
}