Asp.net 做登录验证码（MVC）

  public class ValidateCode
  {
      /// <summary>
        /// 创建随机数
        /// </summary>
        /// <param name="num"></param>
        /// <returns></returns>
        public string CreateRandom(int num)
      {
          string str = "ABCDEFGHJKMNPQRSTUVWXYZabcdefghjkmnpqrstuvwxyz23456789";
          StringBuilder sb = new StringBuilder();
          for (int i = 0; i < num; i++)
          {
              sb.Append(str[new Random(Guid.NewGuid().GetHashCode()).Next(0, str.Length - 1)]);
          }
          return sb.ToString();
      }
      /// <summary>
        /// 验证码图片 => byte[]
        /// </summary>
        /// <param name="verifyCode">验证码</param>
        /// <param name="width">宽</param>
        /// <param name="height">高</param>
        /// <param name="fontsize">字体大小</param>
        /// <returns></returns>
        public byte[] CreateByteByImgVerifyCode(string verifyCode, int width, int height, int fontsize)
      {
          Font font = new Font("Arial", fontsize, (FontStyle.Bold | FontStyle.Italic));
          Brush brush;
          Bitmap bitmap = new Bitmap(width, height);
          Graphics g = Graphics.FromImage(bitmap);
          SizeF totalSizeF = g.MeasureString(verifyCode, font);
          SizeF curCharSizeF;
          PointF startPointF = new PointF(10, (height - totalSizeF.Height) / 2); //x=5开始
            int wx = ((width - 20) / verifyCode.Length); //间距
            Random random = new Random(); //随机数产生器
            g.Clear(Color.White); //清空图片背景色  
            for (int i = 0; i < verifyCode.Length; i++)
          {
              brush = new LinearGradientBrush(new Point(0, 0), new Point(1, 1), Color.FromArgb(random.Next(255), random.Next(255), random.Next(255)), Color.FromArgb(random.Next(255), random.Next(255), random.Next(255)));
              g.DrawString(verifyCode[i].ToString(), font, brush, startPointF);
              curCharSizeF = g.MeasureString(verifyCode[i].ToString(), font);
              startPointF.X += wx;
          }

            //画图片的干扰线  
            for (int i = 0; i < 10; i++)
          {
              int x1 = random.Next(bitmap.Width);
              int x2 = random.Next(bitmap.Width);
              int y1 = random.Next(bitmap.Height);
              int y2 = random.Next(bitmap.Height);
              g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
          }

            //画图片的前景干扰点  
            for (int i = 0; i < 100; i++)
          {
              int x = random.Next(bitmap.Width);
              int y = random.Next(bitmap.Height);
              bitmap.SetPixel(x, y, Color.FromArgb(random.Next()));
          }

          g.DrawRectangle(new Pen(Color.Silver), 0, 0, bitmap.Width - 1, bitmap.Height - 1); //画图片的边框线  
            g.Dispose();

            //保存图片数据  
            MemoryStream stream = new MemoryStream();
          bitmap.Save(stream, ImageFormat.Jpeg);
            //输出图片流  
            return stream.ToArray();

      }
  }

然后做一个接口

 public ActionResult Captcha()
 {
     ValidateCode validateCode = new ValidateCode();
     string code = validateCode.CreateRandom(4);
     Session["code"] = code.ToLower();
     return File(validateCode.CreateByteByImgVerifyCode(code, 130, 48, 22), "image/jpg");
 }

然后前端调用：

  <div style="margin-left: 10px;">
      <img src="/@ViewContext.RouteData.DataTokens["area"]/login/Captcha" class="layadmin-user-login-codeimg" id="LAY-user-get-vercode">
  </div>

如果验证码不出来，可能是服务没有打开，需要打开这个服务

如果没有，请安装一下，这个自行找下