Performance of forensic facial comparison by morphological analysis across optimal and suboptimal CCTV settings

Standardized mounting heights translate to a steep angle of incidence, which reduces image quality and obscures relevant facial detail due to increased subject-to-camera distance and loss of useable resolution.

“The problem with these standardized mounting heights is that they translate to a steep angle of incidence. This in turn reduces image quality and obscures relevant facial detail as a result of the increased SCD and subsequent loss of useable resolution [48,49].”

Eye-level digital CCTV recording-based facial comparisons were almost as accurate (97.3%) and reliable (77.3%) as standardized photograph to unstandardized photograph comparisons.

“In fact, eye-level digital CCTV recording-based facial comparisons were almost as accurate (97.3%) and reliable (77.3%) as the standardized photograph to unstandardized photograph comparisons [21,48] (Figure 2).”

Faces disguised by brimmed caps yielded an exceedingly low CCA (68.1%), yet not as low as the analogue CCTV comparisons (33.1%).

“In contrast, faces disguised by brimmed caps yielded an exceedingly low CCA (68.1%) [49], yet not nearly as low as the analogue CCTV comparisons (33.1%) [48] (Figure 2).”

Analogue CCTV data captured at an angle of incidence of 22° and height of 2.5 m performed worse overall, although it is unclear if this was because of camera position or poor image quality.

“In contrast, our analogue CCTV data, captured at an angle of incidence of 22° and height of 2.5 m, performed worse overall, although it is unclear if this was because of camera position or poor image quality [48].”

In 130 face sets (n = 1300 comparisons) recorded on a low-resolution suboptimal analogue CCTV system, MA had accuracies as low as 33.1%, false negative rates of 75.2%, and reliability of 37.8%.

“The results were found to be much poorer, with accuracies as low as 33.1% with extremely high false negative rates (75.2%) and questionable reliability (37.8%) [48] (Figure 2).”

Eye-level mounted cameras at 1.8 m ground height provide an approximate 0-15° angle of incidence with the subject and provide the most optimal capture of facial detail even with natural head tilt.

“Eye-level mounted cameras at 1.8 m ground height provide an approximate 0–15° angle of incidence with the subject and provide the most optimal capture of facial detail even with natural head tilt [48].”

The performance of MA in faces disguised with sunglasses was markedly high (90.4%), surpassing performance under the same standard CCTV conditions without sunglasses (82.6%), but not better than photographic (99.1%) or eye-level CCTV data (97.3%).

“Overall, the performance of MA in faces disguised with sunglasses was markedly high (90.4%) [49], in fact surpassing the performance of facial comparison under the same standard CCTV conditions without sunglasses (82.6%), but not better than the photographic (99.1%) [21] or eye-level CCTV data (97.3%) [48] (Figure 2).”

Across all of the studies, chance-corrected accuracy (CCA) was the best and most representative measure of accuracy, compared to hit rate and balanced accuracy.

“Across all of our studies, the best measure of accuracy was found to be the chance corrected accuracy (CCA) [21,48,49].”

A strict iteration resulted in worse performance in analogue CCTV comparisons than across all other comparisons (photographs, standard CCTV, and eye-level CCTV).

“A strict iteration resulted in a worse performance in the analogue CCTV comparisons than across all other comparisons (photographs, standard CCTV, and eye-level CCTV) [48].”

All other analyses from the various CCTV and photographic images showed improved performance under a strict iteration.

“All other analyses from the various CCTV and photographic images showed improved performance under a strict iteration [21,48,49].”

MA performance is better and more reliable in a digitally captured sample (IP cameras) at eye-level height (1.7 m) compared with a suboptimal sample at an angle of incidence of 27° (mount height 3.1 m).

“Our reports [48] show an overall better and more reliable performance of MA in a digitally captured sample (IP cameras) at eye-level height (1.7 m) compared with a suboptimal sample at an angle of incidence of 27° (mount height of 3.1 m) [48].”

All forms of facial comparison accuracy will suffer when using low-resolution analogue CCTV images, even if image quality is good in other respects.

“In general, all forms of facial comparison accuracy will suffer when using low-resolution analogue CCTV images, even if image quality is good in other respects [48,81,93,122].”

The conditions in the studies were limited to the major questions broadly investigated by each study.

“In doing so, although realistic, the conditions were limited to the major questions broadly investigated by each study [21,48,49].”

Only two particular CCTV camera specifications under limited conditions and installation variations were tested in our results.

“In consideration of our results, only two particular CCTV camera specifications under limited conditions and installation variations were tested [21,48,49].”

When a face is composed of approximately 18 × 26 pixels or less, such as the analogue CCTV setting employed in our study, FFC analysis would be severely compromised.

“However, based on the actual accuracies and the approximate sizes of faces in each CCTV setting, it would appear that when a face is composed of approximately 18 × 26 pixels or less, such as the analogue CCTV setting employed in our study [48], FFC analysis would be severely compromised.”