Judgment Approved by the court for handing down
R (Bridges) v CCSWP and SSHD
(4) Feature extraction. Taking the faces identified and isolated through
“face detection”, the software automatically extracts unique facial
features from the image of each face, the resulting biometric template
being unique to that image.
(5) Face comparison. The AFR software compares the extracted facial
features with those contained in the facial images held on the watchlist.
(6) Matching. When facial features from two images are compared, the
AFR software generates a “similarity score”. This is a numerical value
indicating the likelihood that the faces match, with a higher number
indicating a greater likelihood of a positive match between the two
faces. A threshold value is fixed to determine when the software will
indicate that a match has occurred. Fixing this value too low or too
high can, respectively, create risks of a high “false alarm rate” (i.e. the
percentage of incorrect matches identified by the software) or a high
“false reject rate” (i.e. the percentage of true matches that are not in
fact matched by the software). The threshold value is generally
suggested by the manufacturer, and depends on the intended use of the
AFR system. It is common to suggest setting the threshold value so
that the False Alarm Rate is 0.1%, 0.01% or 0.001%. Most AFR
systems, however, allow the end user to change the threshold value to
whatever they choose. However, operators of AFR systems are able to
amend the “threshold [of similarity] value”, above which a similarity
score is taken to indicate a potential match.
25.
D.
Thus, whilst use of CCTV cameras is a premise for use of AFR, AFR
technology goes further. A CCTV camera simply captures digital video
recordings. AFR technology uses that digital information to isolate pictures of
individual faces, extract information about facial features from those pictures,
compare that information with the watchlist information, and indicate matches
between faces captured through the CCTV recording and those held on the
watchlist.
SWP’s USE OF AFR
26.
SWP is the police authority which is the national lead on testing and
conducting trials of AFR. The SWP has received grants from the Secretary of
State for this purpose. The SWP has used AFR since mid-2017, and continues
to use it. SWP has a licence to use proprietary AFR software developed by
NEC (now North Gate Public Services (UK) Ltd) called “NeoFace Watch
software”.
27.
SWP uses AFR in two ways5. The first is known as “AFR Identify” under
which images of unknown suspects and persons of interest related to past
5
See, the Evaluation of South Wales Police’s Use of Automatic Facial Recognition
(Cardiff University, Police Science Institute, Crime & Security Research Institute)
(September 2018) (“the UPSI Report”) at pp. 2, 12-15.