Matching views of unfamiliar people how useful are

Matching views of unfamiliar people: how useful are passports and CCTV?

Faces are a primary means of identification: Passports and identity cards CCTV images for identification and prosecution

CCTV cameras are widespread: No good data on how many exist! Mc. Cahill and Norris (2003): 4. 2 million cameras in U. K. "A CCTV camera for every 14 citizens. “ (David Davis, resignation statement, 12 th June 2008) C 4 Fact. Check: highly questionable estimate. Gerrard and Thompson (2008): 1. 85 million (1. 7 million privately owned). Big. Brother. Watch(2012): at least 51, 600 local authoritycontrolled CCTV cameras, at a cost of £ 515 million from 2007 -2011.

Ways in which CCTV might reduce crime (Tilley 1993): Increases chances that offenders will be caught, stopped or punished and therefore deterred. Deters potential offenders who will not want to be observed by CCTV operators or have evidence against them captured on camera. Encourages more "natural surveillance", as more people use the area covered by CCTV. This may deter offenders. Facilitates effective deployment of security staff and police to locations where suspicious behaviour is occurring - either catching or deterring offenders. CCTV cameras and signs show people are taking crime seriously, and thus offenders may be deterred. Publicity about CCTV may encourage potential victims to be more security conscious. Those who are more security-minded may increase their use of areas with CCTV.

Few good data on CCTV’s actual effectiveness – As a deterrent to criminals. Welsh and Farrington (2002): Meta-analysis of 18 studies; half showed benefits, half did not. Gill and Spriggs (2005): Evaluated 13 CCTV systems. Only 2 associated with a signifcant reduction in crime levels. Significant reduction in public anxiety in 3 areas. As prosecution evidence Attorney General’s Reference (2003): if "sufficiently clear", CCTV footage can be used as sole identification evidence.

Matching different views of an unfamiliar face is highly error-prone: Kemp, Towell and Pike (1999): Supermarket credit-card study. Cashiers falsely accepted over 50% of fraudulent cards, and falsely rejected over 10% of legitimate ones. Burton, Wilson, Cowan and Bruce (1999): Subjects judged whether faces seen in high-quality photos had been seen before in video clips. Subjects personally familiar with the targets performed well; subjects unfamiliar with them performed poorly. Henderson, Bruce and Burton (2001): Subjects judged whether each of two "robbers" was shown in video stills - poor performance, with high false identification rates.

Megreya and Burton (2008): Unfamiliar-face matching tasks (using photos or real people, matched to high-quality photographs). Expt 1: short delay Expt 2: simultaneous TP: 70% hits TA: 35% false positives Expt 3: simultaneous, no distractors (passport/ID card matching) 15% error rate, plus bias to say "same" when live TP: 60% hits TA: 20% false positives Little difference between "live" and photo targets; unfamiliar face encoding is poor.

Can jurors reliably match images to suspects? Davis and Valentine (2008): 3 experiments in which a “live” person was shown together with high-quality video. Match between person and video on 50% of trials, mismatch on remainder. Highly error-prone and no better than matching to stills. Worse with disguise, or with year's delay between filming and test. Wide variation between videos overall: 22% of participants made false negative decisions (i. e. saying "different" when actually "same"). 37% failed to identify A as man in video 44% misidentified B as man in video A B 17% of participants made false positive decisions (saying "same" when actually different).

Techniques for "objectively" establishing identity matches – facial mapping: Aim - to determine whether two images show the same person or different people. Normally used where the CCTV image is too poor quality for jurors to decide easily for themselves. Various "Facial Mapping" techniques: Measurements from images (grid overlay, angular measurements, etc. ) Chimeric faces (two image halves juxtaposed) Video wipe techniques (one image progressively overlays another).

Techniques for establishing identity matches – facial mapping by overlaying a grid:

Bromby Scale (2003) used by Facial Mappers to express their opinion on whether a match has been established: Merely a spuriously-quantitative expression of subjective belief, but Atkins vs Queen (2009): does not question the technique's scientific basis; rules that the scale can be used to express the Mapper's opinions.

Techniques for establishing identity matches: photo-anthropometry - angular measurements: Kleinberg, Vanezis and Burton (2007): Calculated different measurements from target faces - six proportion indices (e. g. AA’/BB’) and six angle values (e. g. AB/BB’). Compared each target video image against an array of 10 photos.

Kleinberg, Vanezis and Burton (2007): All measures equally poor, even in these ideal conditions (in real life, = changes in viewpoint, lighting and expression, poor quality video images). Anthropometry is an unreliable technique for matching images.

Davis, Valentine and Davis (2010): Photo-anthropometry tested under ideal conditions: Digital. Face software used to obtain 37 linear and 25 angular measurements from two high-quality images from each of 70 faces (fullface and profile). Compared these to measurements on separate probe images. Identification verification was unreliable unless multiple distance and angular measurements from both views were included.

Biases evoked by techniques used in court by facial mappers (1): Strathie, Mc. Neill and White (2012): Matching is less accurate with aligned chimeras than with full-face images – aligned chimeras evoke holistic processing and a bias towards “same” responses. 88% correct, no bias 73% correct, with “different” bias 67% correct, with “same” bias

Biases evoked by techniques used in court by facial mappers (2): Strathie and Mc. Neill (2012): Matching is less accurate with video "wipes" than with full-face images – bias towards “same” responses. (A possibility noted by Vanezis and Brierley, 1996).

Conclusions: Technological limitations of CCTV: Wide-angle lenses distort images Cameras often positioned high, giving foreshortened views Poor lighting conditions Poor image resolution, especially with data-compression – images inherently lack information Criminals use disguises Psychological limitations of unfamiliar face-matching: Even under ideal conditions, unfamiliar face-matching is poor. Dangers of facial mapping techniques: Facial mapping techniques are unreliable and should not be admissible as evidence in court (Mc. Neill and Strathie 2012). Facial mapping evidence reduces jurors’ (already poor) ability to match CCTV images to defendants.