https://guide.jinbo.net/workplacesurveillance/4%ec%9e%a5-%ea%b0%90%ec%8b%9c%ec%84%a4%eb%b9%84-%eb%8f%84%ec%9e%85%ec%97%90-%eb%8c%80%ed%95%9c-%eb%8c%80%ec%9d%91-%eb%b0%a9%ec%95%88/