调用百度的接口，每月有一千次的免费额度，百度的接口文档写得真好啊。。代码全列出来，复制粘贴就好了

using System;
using System.IO;
using RestSharp;//依赖版本106.15.0 https://www.nuget.org/packages/RestSharp/106.15.0
using Newtonsoft.Json; //https://www.nuget.org/packages/Newtonsoft.Json

namespace OrcTest
{

 
        public class Program
        {

            const string API_KEY = "2G6YLMnNfochiBm7APGffY0P";
            const string SECRET_KEY = "gElZS22qsMShdHheh2iY48em0WZYgF5j";

            public static void Main(string[] args)
            {
                var client = new RestClient($"https://aip.baidubce.com/rest/2.0/ocr/v1/accurate_basic?access_token={GetAccessToken()}");
                 client.Timeout = -1;
                var request = new RestRequest(Method.POST);
                request.AddHeader("Content-Type", "application/x-www-form-urlencoded");
                request.AddHeader("Accept", "application/json");
                request.AddParameter("url", "http://www.niunan.net/images/orctest.jpg");
                request.AddParameter("detect_direction", "false");
                request.AddParameter("paragraph", "false");
                request.AddParameter("probability", "false");
                IRestResponse response = client.Execute(request);
                Console.WriteLine(response.Content);

            }


            /**
            * 使用 AK，SK 生成鉴权签名（Access Token）
            * @return 鉴权签名信息（Access Token）
            */
            static string GetAccessToken()
            {
                var client = new RestClient($"https://aip.baidubce.com/oauth/2.0/token") ;
           
               client.Timeout = -1;
                var request = new RestRequest(Method.POST);
                request.AddParameter("grant_type", "client_credentials");
                request.AddParameter("client_id", API_KEY);
                request.AddParameter("client_secret", SECRET_KEY);
                IRestResponse response = client.Execute(request);
                Console.WriteLine(response.Content);
                var result = JsonConvert.DeserializeObject<dynamic>(response.Content);
                return result.access_token.ToString();
            }

        }
 

}