WinForm generates random verification code

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

namespace  Generate random verification code 
{
    
    public partial class Form1 : Form
    {
    
        public Form1()
        {
    
            InitializeComponent();
        }
        string path = Application.StartupPath;
        string filename = "code.png";
        private void button1_Click(object sender, EventArgs e)
        {
    
           
            string data= MakeCode(4);
            textBox1.Text= data;
            MemoryStream memoryStream= CheckCodeImage(data);
            
			// Write pictures locally   Use it if you want   Delete here if you don't want to save 
            FileStream file = new FileStream(Path.Combine(path,filename), FileMode.OpenOrCreate);
            file.Write(memoryStream.GetBuffer(), 0, memoryStream.GetBuffer().Length);
            file.Close();// Close file 
			
			// Display in picture area 
            Image image = Image.FromStream(memoryStream);
            pictureBox1.Image = image;
            pictureBox1.Size = new Size(image.Width, image.Height);
        }
        /// <summary>
        ///  Generate random verification code numbers + Letter 
        /// </summary>
        /// <param name="codelen"> Length of verification code </param>
        /// <returns> Return verification code </returns>
        public static string MakeCode(int codelen)
        {
    
            if (codelen < 1)
            {
    
                return string.Empty;
            }
            int number;
            StringBuilder strCheckCode = new StringBuilder();
            Random random = new Random();
            for (int index = 0; index < codelen; index++)
            {
    
                number = random.Next();
                if (number % 2 == 0)
                {
    
                    strCheckCode.Append((char)('0' + (char)(number % 10)));// Generating random numbers 
                }
                else
                {
    
                    strCheckCode.Append((char)('A' + (char)(number % 26)));// Generate random letters 
                }
            }
            return strCheckCode.ToString();
        }
        public static MemoryStream CheckCodeImage(string CheckCode)
        {
    
            if (string.IsNullOrEmpty(CheckCode))
            {
    
                return null;
            }
            Bitmap image = new Bitmap((int)Math.Ceiling((CheckCode.Length * 12.5)), 22);
            Graphics graphic = Graphics.FromImage(image);// Create a captcha image 
            try
            {
    
                Random random = new Random();
                graphic.Clear(Color.White);
                int x1 = 0, y1 = 0, x2 = 0, y2 = 0;
                for (int index = 0; index < 25; index++)
                {
    
                    x1 = random.Next(image.Width);
                    x2 = random.Next(image.Width);
                    y1 = random.Next(image.Height);
                    y2 = random.Next(image.Height);
                    graphic.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
                }
                Font font = new Font("Arial", 12, (FontStyle.Bold | FontStyle.Italic));//Font Set the font , Font size , The font 
                                                                                       // Set the start color and end color of the graphic gradient , Gradient angle 
                LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Red, Color.DarkRed, 1.2f, true);
                graphic.DrawString(CheckCode, font, brush, 2, 2);
                int X = 0; int Y = 0;
                // Draw the foreground noise of the picture 
                for (int i = 0; i < 100; i++)
                {
    
                    X = random.Next(image.Width);
                    Y = random.Next(image.Height);
                    image.SetPixel(X, Y, Color.FromArgb(random.Next()));
                }
                // Draw the border line of the picture 
                graphic.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);
               
                // Save the picture as stream Stream return 
                MemoryStream ms = new MemoryStream();
                image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
                return ms;
            }
            finally
            {
    
                graphic.Dispose();
                image.Dispose();
            }
        }
    }
}