C# WinForm 登录界面的图片验证码(区分大小写+不区分大小写)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Drawing;//图片
using System.Windows.Forms;

namespace ValidCodeTest
{
  public class Class1
  {
    #region 验证码功能      
    /// <summary>
    /// 生成随机验证码字符串
    /// </summary>
    public static string CreateRandomCode(int CodeLength) 
    {
      int rand;
      char code;
      string randomCode = String.Empty;//随机验证码
     	
     	//生成一定长度的随机验证码    
      //Random random = new Random();//生成随机数对象
      for (int i = 0; i < CodeLength; i++)
      {
        //利用GUID生成6位随机数   
        byte[] buffer = Guid.NewGuid().ToByteArray();//生成字节数组
        int seed = BitConverter.ToInt32(buffer, 0);//利用BitConvert方法把字节数组转换为整数
        Random random = new Random(seed);//以生成的整数作为随机种子
        rand = random.Next();

        //rand = random.Next();   
        if (rand % 3 == 1)
        {
          code = (char)('A' + (char)(rand % 26));
        }
        else if (rand % 3 == 2)
        {
          code = (char)('a' + (char)(rand % 26));          
        }
        else
        {
          code = (char)('0' + (char)(rand % 10));
        }
        randomCode += code.ToString();
      }
      return randomCode;
    }

    /// <summary>
    /// 创建验证码图片
    /// </summary>
    public static void CreateImage(string strValidCode, PictureBox pbox)
    {
      try
      {
        int RandAngle = 45;//随机转动角度
        int MapWidth = (int)(strValidCode.Length * 21);
        Bitmap map = new Bitmap(MapWidth, 28);//验证码图片—长和宽

				//创建绘图对象Graphics
        Graphics graph = Graphics.FromImage(map);
        graph.Clear(Color.AliceBlue);//清除绘画面,填充背景色
        graph.DrawRectangle(new Pen(Color.Black, 0), 0, 0, map.Width - 1, map.Height - 1);//画一个边框
        graph.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;//模式
        Random rand = new Random();
        //背景噪点生成
        Pen blackPen = new Pen(Color.LightGray, 0);
        for (int i = 0; i < 50; i++)
        {
          int x = rand.Next(0, map.Width);
          int y = rand.Next(0, map.Height);
          graph.DrawRectangle(blackPen, x, y, 1, 1);
        }
        //验证码旋转，防止机器识别
        char[] chars = strValidCode.ToCharArray();//拆散字符串成单字符数组
        //文字居中
        StringFormat format = new StringFormat(StringFormatFlags.NoClip);
        format.Alignment = StringAlignment.Center;
        format.LineAlignment = StringAlignment.Center;
        //定义颜色
        Color[] c = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple };
        //定义字体
        string[] font = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial", "宋体" };
        for (int i = 0; i < chars.Length; i++)
        {
          int cindex = rand.Next(7);
          int findex = rand.Next(5);
          Font f = new System.Drawing.Font(font[findex], 13, System.Drawing.FontStyle.Bold);//字体样式(参数2为字体大小)
          Brush b = new System.Drawing.SolidBrush(c[cindex]);
          Point dot = new Point(16, 16);

          float angle = rand.Next(-RandAngle, RandAngle);//转动的度数
          graph.TranslateTransform(dot.X, dot.Y);//移动光标到指定位置
          graph.RotateTransform(angle);
          graph.DrawString(chars[i].ToString(), f, b, 1, 1, format);

          graph.RotateTransform(-angle);//转回去
          graph.TranslateTransform(2, -dot.Y);//移动光标到指定位置
        }
        pbox.Image = map;
      }
      catch (ArgumentException)
      {
        MessageBox.Show("验证码图片创建错误");
      }
    }
    #endregion
  }
}

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using ValidCodeTest;

namespace ValidCode
{
  public partial class Form1 : Form
  {
    public Form1()
    {
      InitializeComponent();
    }


    #region 验证码
    private const int ValidCodeLength = 4;//验证码长度    
    private String strValidCode = "";//验证码            

    //调用自定义函数,更新验证码
    private void UpdateValidCode()
    {
      strValidCode = Class1.CreateRandomCode(ValidCodeLength);//生成随机验证码
      if (strValidCode == "") return;
      Class1.CreateImage(strValidCode, pbox1);//创建验证码图片
    }
    #endregion


    private void pbox1_Click(object sender, EventArgs e)
    {
      UpdateValidCode();//点击更新验证码
    }


    private void Form1_Load(object sender, EventArgs e)
    {
      UpdateValidCode();//加载更新验证码
    }


    /// <summary>
    /// 验证（区分大小写）
    /// </summary>    
    private void btn1_Click(object sender, EventArgs e)
    {
      string validcode = txtValidCode.Text.Trim();

      char[] ch1 = validcode.ToCharArray();
      char[] ch2 = strValidCode.ToCharArray();
      int Count1 = 0;//字母个数
      int Count2 = 0;//数字个数

      if (String.IsNullOrEmpty(validcode) != true)//验证码不为空
      {
        for (int i = 0; i < strValidCode.Length; i++)
        {
          if ((ch1[i] >= 'a' && ch1[i] <= 'z') || (ch1[i] >= 'A' && ch1[i] <= 'Z'))//字母
          {
            if (ch1[i] == ch2[i])
            {
              Count1++;
            }
          }
          else//数字
          {
            if (ch1[i] == ch2[i])
            {
              Count2++;
            }
          }

        }

        int CountSum = Count1 + Count2;
        if (CountSum == strValidCode.Length)
        {
          MessageBox.Show("验证通过", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
          UpdateValidCode();
          txtValidCode.Text = "";
          txtValidCode.Focus();
        }
        else
        {
          MessageBox.Show("验证失败", "警告", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
          UpdateValidCode();//更新验证码
          txtValidCode.Text = "";
          txtValidCode.Focus();
        }
      }
      else//验证码为空
      {
        MessageBox.Show("请输入验证码", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
        UpdateValidCode();//更新验证码
        txtValidCode.Text = "";
        txtValidCode.Focus();
      }
    }


    /// <summary>
    /// 验证（不区分大小写）
    /// </summary> 
    private void btn2_Click(object sender, EventArgs e)
    {
      string validcode = txtValidCode.Text.Trim();

      if (String.IsNullOrEmpty(validcode) != true)//验证码不为空
      {
        if (validcode.ToLower() == strValidCode.ToLower())
        {
          MessageBox.Show("验证通过", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
          UpdateValidCode();
          txtValidCode.Text = "";
          txtValidCode.Focus();
        }
        else
        {
          MessageBox.Show("验证失败", "警告", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
          UpdateValidCode();//更新验证码
          txtValidCode.Text = "";
          txtValidCode.Focus();
        }
      }
      else//验证码为空
      {
        MessageBox.Show("请输入验证码", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
        UpdateValidCode();//更新验证码
        txtValidCode.Text = "";
        txtValidCode.Focus();
      }
    }
  }
}