A key component of any FRT system is the underlying database of images the system matches to. The use of images collected when individuals are taken into custody is of concern; there are over 19 million images in the Police National Computer (PNC) database. I am also considering the transparency and proportionality of retaining these photographs as a separate issue, particularly for those arrested but not charged for certain offences. The Biometrics Commissioner has also raised these concerns.
Source:
https://iconewsblog.org.uk/2018/05/14/facial-recognition-technology-and-law-enforcement/
Face recognition must need a data base underlying in the backend system and might have abusing case so it one of the concerning issue in the privacy area.