一、核心应用场景
- 用户登录/注册验证：防止恶意程序批量注册
- 表单提交防护：确保关键操作由真人执行
- API接口限流：抵御自动化脚本攻击
- 敏感操作验证：如支付、信息修改等关键步骤
- 数据防爬机制：保护网站内容不被爬虫抓取
二、技术实现方案
1. 基础架构设计
// 验证码服务架构 +------------------------+ | 验证码生成模块 | ← 随机字符 | (CaptchaGenerator) | +------------------------+↓ +------------------------+ | 图像处理模块 | ← 添加干扰元素 | (ImageProcessor) | +------------------------+↓ +------------------------+ | 验证码存储模块 | → Redis/Session | (CaptchaStorage) | +------------------------+
2. 完整实现代码（ASP.NET MVC）
using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Web.Mvc;namespace CaptchaDemo.Controllers
{public class CaptchaController : Controller{/// <summary>/// 生成验证码图片（带干扰元素）/// </summary>[HttpGet]public ActionResult Generate(int width = 120, int height = 40){// 生成随机验证码（4-6位）string captchaCode = GenerateRandomCode(4);// 创建位图对象using (Bitmap bitmap = new Bitmap(width, height)){using (Graphics g = Graphics.FromImage(bitmap)){// 设置画布属性g.Clear(Color.WhiteSmoke);g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;// 添加干扰线（5-8条）AddNoiseLines(g, width, height);// 绘制验证码文字DrawCaptchaText(g, captchaCode, width, height);// 添加噪点（100-200个）AddNoisePoints(bitmap, width, height);}// 输出图片流using (MemoryStream stream = new MemoryStream()){bitmap.Save(stream, ImageFormat.Jpeg);return File(stream.ToArray(), "image/jpeg");}}}/// <summary>/// 生成随机验证码（包含数字和字母）/// </summary>private string GenerateRandomCode(int length){const string chars = "23456789ABCDEFGHJKLMNPQRSTUVWXYZ"; // 排除易混淆字符Random random = new Random(Guid.NewGuid().GetHashCode());char[] result = new char[length];for (int i = 0; i < length; i++){result[i] = chars[random.Next(chars.Length)];}return new string(result);}/// <summary>/// 绘制干扰线/// </summary>private void AddNoiseLines(Graphics g, int width, int height){Random random = new Random();for (int i = 0; i < 6; i++){int x1 = random.Next(width);int y1 = random.Next(height);int x2 = random.Next(width);int y2 = random.Next(height);g.DrawLine(new Pen(Color.FromArgb(random.Next(128, 256),random.Next(128, 256),random.Next(128, 256))), x1, y1, x2, y2);}}/// <summary>/// 绘制验证码文字（带旋转效果）/// </summary>private void DrawCaptchaText(Graphics g, string code, int width, int height){Random random = new Random();float charWidth = width / (code.Length + 1);for (int i = 0; i < code.Length; i++){// 设置随机颜色Brush brush = new SolidBrush(Color.FromArgb(random.Next(50, 150),random.Next(50, 150),random.Next(50, 150)));// 随机旋转角度（-30°到30°）g.TranslateTransform(charWidth * i + charWidth / 2, height / 2);g.RotateTransform(random.Next(-30, 30));// 绘制文字g.DrawString(code[i].ToString(),new Font("Arial", 18, FontStyle.Bold),brush,new PointF(-charWidth / 3, -10),StringFormat.GenericTypographic);// 重置变换矩阵g.ResetTransform();}}/// <summary>/// 添加噪点/// </summary>private void AddNoisePoints(Bitmap bitmap, int width, int height){Random random = new Random();for (int i = 0; i < 150; i++){int x = random.Next(width);int y = random.Next(height);bitmap.SetPixel(x, y, Color.FromArgb(random.Next(256),random.Next(256),random.Next(256)));}}}
}三、前端集成教程
1. HTML视图代码
<div class="captcha-box"><img id="captchaImg" src="@Url.Action("Generate", "Captcha")" onclick="refreshCaptcha()" title="点击刷新验证码"/><input type="text" id="captchaInput" placeholder="输入验证码"/>
</div>2. JavaScript交互
function refreshCaptcha() {// 添加时间戳防止缓存let timestamp = new Date().getTime();document.getElementById('captchaImg').src = '@Url.Action("Generate", "Captcha")?t=' + timestamp;
}// 表单提交验证示例
function validateCaptcha() {let userInput = document.getElementById('captchaInput').value;fetch('/Captcha/Validate?code=' + userInput).then(response => {if(!response.ok) throw new Error('验证码错误');// 后续提交逻辑...});
}四、服务端验证实现
/// <summary>
/// 验证码校验（需配合Session或Redis存储）
/// </summary>
[HttpPost]
public ActionResult Validate(string code)
{string sessionCode = Session["CaptchaCode"]?.ToString();if(string.IsNullOrEmpty(sessionCode))return Json(new { success = false, message = "验证码已过期" });bool isValid = code.Equals(sessionCode, StringComparison.OrdinalIgnoreCase);// 验证后清除SessionSession.Remove("CaptchaCode");return Json(new { success = isValid });
}（注：实际部署时需要根据大家的实际情况添加异常处理和日志记录模块）