API : https://api.weixin.qq.com/wxa/servicemarket?access_token

params = {

      "service": "wx79ac3de8be320b71",

      "api": "OcrAllInOne",

      "data": {

        "img_data": "",

        "data_type": 2,

        "ocr_type": 1

      },

      "client_msg_id": "id123"

    };

    $.ajax({

      type: "POST",

      url: "https://api.weixin.qq.com/wxa/servicemarket?access_token=token",

      contentType: "application/json",

      data: JSON.stringify(params),  //此处注意，要转换成JSON.stringify(对象)

      dataType: "json",

      success: function (data) {

      },

      error: function (data) {

      }

    });