借鉴了网上的各种方案，都是同样的结果：

云函数如下：

exports.main = async (event, context) => {
  const fileID = event.fileID
  const res = await cloud.downloadFile({
    fileID: fileID,
  })
  const buffer = res.fileContent
  try {
    var result = await cloud.openapi.security.imgSecCheck({
      media: {
        contentType: 'image/png',
        value: buffer
      }
    });
    return result
  } catch (err) {
    return err
  }
}