.net core第三方图形验证

asp.net core是否提供第三方图形验证库的示例？我正在研究这个，但我查了一些资料但没有成功，请给我一些例子！谢谢。 供我参考，还有其他好的库吗？

https://tutexchange.com/how-to-implement-captcha-in-asp-net-core/

您可以使用Bitmap库生成图形验证码。首先，创建一个生成的工具类。代码如下：

public class VerifyCodeHelper
    {
        public static Bitmap CreateVerifyCode(out string code)
        {
            //Create a Bitmap object and draw
            Bitmap bitmap = new Bitmap(200, 60);
            Graphics graph = Graphics.FromImage(bitmap);
            graph.FillRectangle(new SolidBrush(Color.White), 0, 0, 200, 60);
            Font font = new Font(FontFamily.GenericSerif, 48, FontStyle.Bold, GraphicsUnit.Pixel);
            Random r = new Random();
            string letters = "0123456789";

            StringBuilder sb = new StringBuilder();

            //Add random 4 numbers
            for (int x = 0; x < 4; x++)
            {
                string letter = letters.Substring(r.Next(0, letters.Length - 1), 1);
                sb.Append(letter);
                graph.DrawString(letter, font, new SolidBrush(Color.Black), x * 38, r.Next(0, 15));
            }
            code = sb.ToString();

            //Confuse the background
            Pen linePen = new Pen(new SolidBrush(Color.Black), 2);
            for (int x = 0; x < 6; x++)
                graph.DrawLine(linePen, new Point(r.Next(0, 199), r.Next(0, 59)), new Point(r.Next(0, 199), r.Next(0, 59)));
            return bitmap;
        }

    }

努吉特包：

<ItemGroup>
    <PackageReference Include="System.Drawing.Common" Version="6.0.0" />
  </ItemGroup>

控制器：

 [ApiController]
    public class VerifyCodeController : Controller
    {
        private readonly IDistributedCache _distributedCache;

        public VerifyCodeController(IDistributedCache distributedCache)
        {
            _distributedCache = distributedCache;
        }

        [Route("get_captcha")]
        public Object VerifyCode()
        {
            string code = "";
            Bitmap bitmap = VerifyCodeHelper.CreateVerifyCode(out code);
            _distributedCache.SetString("code", code);

            base.HttpContext.Session.SetString("CheckCode", code);
            MemoryStream stream = new MemoryStream();
            bitmap.Save(stream, ImageFormat.Gif);
            return File(stream.ToArray(), "image/gif");
        }
    }

startup.cs配置：（如果api调用异常，请仔细检查配置）

public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllers();
            services.AddDistributedMemoryCache();
            services.AddSession(options => {
                options.IdleTimeout = TimeSpan.FromMinutes(1);
            });
            services.AddMvc();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseHttpsRedirection();

            app.UseRouting();

            app.UseAuthorization();

            app.UseStaticFiles();
            app.UseSession();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }
    }

调用 get_captcha 路由：

更多自定义用法可以参考这篇文章：

.Net Core Bitmap 位图处理