/// <summary>
  /// 获取验证码
  /// </summary>
  public List<VerificationCode.Model.WenZhi> GetCodeText()
  {
   const string sql = "SELECT * FROM wenzhi ORDER BY RAND() LIMIT 4";
   var dataReader = dbHelper.GetDataReader(sql);
   var list = DataReaderToList(dataReader);
   dataReader.Close();
   return list;
  } 

  /// <summary>
  /// 获取答案备选
  /// </summary>
  /// <param name="buShouCode">部首编码</param>
  /// <param name="id">当前文字ID</param>
  /// <param name="number">数量</param>
  /// <returns></returns>
  public List<VerificationCode.Model.WenZhi> GetAnswer(string buShouCode, int id,int number=1)
  {
   string sql = $"SELECT * FROM wenzhi where BuShouCode='{buShouCode}' and ID <> {id} ORDER BY RAND() LIMIT "+ number;
   var dataReader = dbHelper.GetDataReader(sql);
   var list = DataReaderToList(dataReader);
   dataReader.Close();
   return list;
  } 

 public Model.Code GetCode()
  {
   
   var wenzlist = _wenZhiDal.GetCodeText(); //获取验证码
   var listAnsuwr = new List<Answer>();//实例化备选答案对象
   var answerCode = string.Empty;//答案
   var result = new Model.Code
   {
    Id = Guid.NewGuid().ToString()
   };
   //根据验证码获取备选答案并把添加到答案添加到备选答案集合
   foreach (var item in wenzlist)
   {
    answerCode += item.ID + ",";
    result.AnswerValue += item.Text;
    var answerList = _wenZhiDal.GetAnswer(item.BuShouCode, item.ID);
    listAnsuwr.Add(new Answer { Id = item.ID.ToString(), Img = GetImage(item.Text) });
    listAnsuwr.AddRange(answerList.Select(answer => new Answer { Id = answer.ID.ToString(), Img = GetImage(answer.Text) }));
   }
   //如果答案个数不够就再去取几个
   if (listAnsuwr.Count < 9)
   {
    var ran = new Random();
    var randKey = ran.Next(0, 4);
    var item = wenzlist[randKey];
    var answerList = _wenZhiDal.GetAnswer(item.BuShouCode, item.ID, 9 - listAnsuwr.Count);
    listAnsuwr.AddRange(answerList.Select(answer => new Answer { Id = answer.ID.ToString(), Img = GetImage(answer.Text) }));
   }
   result.CodeImg = GetImage(result.AnswerValue);//获取图片
   result.AnswerValue = answerCode.TrimEnd(',');
   result.Answer = RandomSortList(listAnsuwr);//打乱正确答案与形近字的顺序
   return result;
  } 

  /// <summary>
  /// 随机排列集合
  /// </summary>
  /// <typeparam name="T"></typeparam>
  /// <param name="listT"></param>
  /// <returns></returns>
  private static List<T> RandomSortList<T>(IEnumerable<T> listT)
  {
   var random = new Random();
   var newList = new List<T>();
   foreach (var item in listT)
   {
    newList.Insert(random.Next(newList.Count + 1), item);
   }
   return newList;
  } 

private static string GetImage(string text)
  {
   Image image;
   switch (text.Length)
   {
    case 1:
     image = new Bitmap(50, 40);
     break;
    case 4:
     image = new Bitmap(120, 40);
     break;
    default:
     image = new Bitmap(50, 40);
     break;
   }
   Brush brushText = new SolidBrush(Color.FromArgb(255, 0, 0, 0));
   var graphics = Graphics.FromImage(image);
   graphics.SmoothingMode = SmoothingMode.AntiAlias;
   graphics.Clear(Color.White);
   var font = new Font(new FontFamily("华文彩云"), 20, FontStyle.Regular);
   if (text.Length > 1)//画验证码
   {
    //先来两条直线做干扰 然后再画文字
    graphics.DrawLine(new Pen(brushText, new Random().Next(1, 3)), new Point(new Random().Next(0, 10), new Random().Next(10, 40)), new Point(new Random().Next(100, 120), new Random().Next(10, 30)));
    graphics.DrawLine(new Pen(brushText, new Random().Next(1, 3)), new Point(new Random().Next(20, 50), new Random().Next(0, 10)), new Point(new Random().Next(100, 120), new Random().Next(30, 40)));
    graphics.DrawString(text, font, brushText, 0, 10);

   }
   else//画备选答案
   {
    Point middle = new Point(25, 20);
    graphics.TranslateTransform(middle.X, middle.Y);
    //这里是360°随机旋转 
    graphics.RotateTransform(new Random().Next(0, 360));
    var format = new StringFormat(StringFormatFlags.NoClip)
    {
     Alignment = StringAlignment.Center,
     LineAlignment = StringAlignment.Center
    };
    graphics.DrawString(text, font, brushText, 0, 0, format);

   }
   brushText.Dispose();
   graphics.Dispose();
   return ImageToBase64(image);
  } 

  public string GetVerCode()
  {
   var code = new VerificationCode.Code().GetCode();
   Session["VERCODE"] = code.AnswerValue;
   code.AnswerValue = "";
   return JsonConvert.SerializeObject(code);
  } 

<div class="form-group">
     <ul class="vercode">
      <li><img src=''/></li>
      <li><img src=''/></li>
      <li><img src=''/></li>
      <li><img src=''/></li>
      <li class="delete" onclick="delete_input()"></li>
     </ul>
     <div>
      <img id="code-image"/> <a href="javascript:void(0);" onclick="load_vercode()">看不清？</a>
     </div>
     <ul class="vercode-anwser">
      <li><img /></li>
      <li><img /></li>
      <li><img /></li>
      <li><img /></li>
      <li><img /></li>
      <li><img /></li>
      <li><img /></li>
      <li><img /></li>
      <li><img /></li>
     </ul>
    </div> 

<script>
  $(function () {
   //加载验证码
   load_vercode();
   //绑定验证码点击事件
   $(".vercode-anwser").find("img").on("click", null, function () {
    $(".vercode").find("img[src='']:eq(0)").attr("src", $(this).attr("src"));
   });
  });

  function load_vercode() {
   $(".vercode").find("img").attr("src", "");
   $.get("GetVerCode", function (data) {
    var result = JSON.parse(data);
    $("#code-image").attr("src", "data:image/png;base64," + result.CodeImg);
    $(".vercode-anwser").find("img").each(function (index) {
     $(this).attr("src", "data:image/png;base64," + result.Answer[index].Img);
    });
   });
  }
  //删除事件
  function delete_input() {
   $(".vercode").find("img[src!='']:last").attr("src", "");
  }
 </script>