不知道问题出在哪里？
一、云函数部分
config.json:
{
  "permissions": {
    "openapi": [
      "security.imgSecCheck"
    ]
  }
}
index.js:
// 云函数入口文件
const cloud = require('wx-server-sdk');
cloud.init({env:cloud.DYNAMIC_CURRENT_ENV,})
// 云函数入口函数
exports.main = async(event, context) => {
  try {
    const result = await cloud.openapi.security.imgSecCheck({
      media:{
        header:{'Content-Type':'application/octet-stream'},
        contentType:'image/png',
        value:Buffer.from(event.value)// Buffer.from()是必须的
      }
    })
    return result
  } catch (err) {
    return err
  }
}

二、前端js：
    onUploadImg: function () {
    wx.chooseImage({
      count: 1,
      sizeType: ['original', 'compressed'],
      sourceType: ['album', 'camera'],
      success:res =>{
        const filePaths = res.tempFilePaths[0]
        if(filePaths && filePaths > 1024*1024){
          tips('图片不能大于1M')
          return
        }
        console.log('res.tempFilePaths[0]: ',res.tempFilePaths[0])
        wx.getFileSystemManager().readFile({
          encoding:'base64',
          filePath:filePaths,          
          success:res => {
            var buffer = res.data
            tips('图片检测中')
            console.log('readFile: ',buffer)
            wx.cloud.callFunction({
              name:'imgCheck',
              data:{
                value:buffer
              },
              success : res1 => {
                console.log('1: ',res1.result)
                if(res1.result.errCode == 0){
                }
                if(res1.result.errCode == 87014){
                }
              },
              fail:err => {
              }
            })
          }
        })
      }    
    })
  },