Craniofacial Superimposition: Historical Review and Current Issues

The Critical Photographic Variables Contributing to Skull-Face Superimposition Methods to Assist Forensic Identification of Skeletons: A Review

When an unidentified skeleton is discovered, a video superimposition (VS) of the skull and a facial photograph may be undertaken to assist identification. In the first instance, the method is fundamentally a photographic one, requiring the overlay of two 2D photographic images at transparency for comparison. Presently, mathematical and anatomical techniques used to compare skull/face anatomy dominate superimposition discussions, however, little attention has been paid to the equally fundamental photographic prerequisites that underpin these methods. This predisposes error, as the optical parameters of the two comparison photographs are (presently) rarely matched prior to, or for, comparison. In this paper, we: (1) review the basic but critical photographic prerequisites that apply to VS; (2) propose a replacement for the current anatomy-centric searches for the correct 'skull pose' with a photographic-centric camera vantage point search; and (3) demarcate superimposition as a clear two-stage phased procedure that depends first on photographic parameter matching, as a prerequisite to undertaking any anatomical comparison(s).

Perspective distortion tolerances and skull-face registration in craniofacial superimposition: an analytical review

Craniofacial superimposition requires the photographic registration of a skull at transparency to a photograph of an antemortem (AM) face so that anatomical concordance between the two can be assessed. When the camera vantage point of the AM photograph is exactly replicated for skull photography, the superimposition is a relatively straightforward process as the images are precisely comparable without complicating factors. In practice, however, focus distances are almost never exactly replicated because the focus distance for AM face photography is rarely known. Embedded differences in perspective, thereby, drive the images away from correspondence, raising questions as to how much difference can be tolerated and what image registration methods should be used. Recently, a ± 1% mismatch in facial height has been posited as an acceptable upper tolerance limit to differential perspective, but this proposition is speculative and has not yet been confirmed by tests on real-life images. In addition, the impact of image registration methods, though critically relevant, has received comparatively little consideration. This paper provides the first in-depth review of these intertwined perspective/registration matters and objective evaluation of tolerances by using real 2D photographic images and synthetic images generated from 3D CT data to demonstrate perspective impact on skull morphology. Taken together, the review confirms a ≤ 1% perspective difference in facial height to be a suitable criterion for craniofacial superimposition (at least as a starting point for method improvement), and that image registration should be point-based using a sellion/nasion combination to minimize anatomical misalignment in the principal region-of-interest (the mid-face).

Focus distance estimation from photographed faces: a test of PerspectiveX using 1709 frontal and profile photographs from DSLR and smartphone cameras

As focus distance (FD) sets perspective, it is an important consideration for the forensic analysis of faces in photographs, including those used for craniofacial superimposition. In the craniofacial superimposition domain, the PerspectiveX algorithm has been suggested for FD estimation. This algorithm uses a mean value of palpebral fissure length, as a scale, to estimate the FD. So far, PerspectiveX has not been validated for profile view photographs or for photographs taken with smartphones. This study tests PerspectiveX in both front and profile views, using multiple DSLR cameras, lenses and smartphones. In total, 1709 frontal and 1709 profile photographs of 10 adult participants were tested at 15 ground truth FDs using three DSLR cameras with 12 camera/lens combinations, five smartphone back cameras and four smartphone front cameras. Across all distances, PerspectiveX performed with a mean absolute error (MAE) of 11% and 12% for DSLR photographs in frontal and profile views, respectively, while errors doubled for frontal and profile photographs from smartphones (26% and 27%, respectively). This reverifies FD estimation for frontal DSLR photographs, validates FD estimates from profile view DSLR photographs and shows that FD estimation is currently inaccurate for smartphones. Until such time that FD estimations for facial photographs taken using smartphones improves, DSLR or 35 mm film images should continue to be sought for craniofacial superimpositions.

Methods of forensic facial reconstruction and human identification: historical background, significance, and limitations

Facial reconstruction is the most frequently used method for human identification in forensic examinations. It is a complex and time-consuming technique and an actively growing field with a wide array of applications. The methods of forensic facial reconstruction are helpful in those cases where other methods of identification are not applicable. Identification of the dead is always a challenging task for forensic teams in cases involving terrorists' attacks and mass disasters where the corpses are fragmented, decomposed, and skeletonized. In such cases, only the skeletal remains and few other clues are available to establish the identity of a person. The progress of facial reconstruction was initiated in the nineteenth century, reconstructing the facial profiles of some famous and rich people. Various novel techniques for facial reconstruction have been devised in the recent past. We conducted literature search, using databases PubMed, Scopus, Web of Science, and ScienceDirect for analyzing different methods developed and practiced till date for human facial reconstruction. We outline the brief history along with a discussion regarding the different methods of forensic facial reconstruction and their limitations. We also discuss future recommendations and preferences for further research in the field of forensic facial reconstruction and human identification.

Facial Soft Tissue Thickness Differences among Three Skeletal Classes in Korean Population Using CBCT

Studies related to facial soft tissue thickness (FSTT) have been conducted since the late 19th century. Soft tissue is any tissue in the body that is not hardened by ossification or calcification processes, such as bones and teeth; and varies according to sex, age, race, and nutritional status. Forensically, soft tissue thickness plays an important role in cases where a cadaver has no unique characteristics; and the remains cannot be identified through DNA analysis, fingerprints, or examination of dental records. Therefore, the results of the current study suggest that the average thickness of the three skeletal classes (i.e., straight, concave, and convex) should be used for face restoration and forensic art research. It is thought that the current study's results will be invaluable in the fields of forensic science, forensic art, anthropology, and dentistry. As a result, gender differences were observed in all classes, and the facial tissue thickness in Korean adults differed according to gender and occlusion type.

The nose as a feature of forensic practice

The nose is a prominent facial structure which is too often overlooked by forensic medicine practitioners. Studies that consider the role of the nose in forensic practice are scattered throughout scientific literature. We provide a brief review of these.

Craniofacial superimposition: a review of focus distance estimation methods and an extension to profile view photographs

Craniofacial superimposition concerns the photographic overlay of skulls and faces, for skeletal identification. As a phased method that depends on photographic optics first and anatomical comparisons second, superimposition is strongly underpinned by the physics of light travel through glass lenses. So that the downstream (and dependent) anatomical evaluations are not thwarted or erroneous identification decisions risked, it is critical that the optical prerequisites for valid image comparisons are met. As focus distance sets the perspective, the focus distance used for skull photography must be matched to that used at face photography, so that anatomically comparable 1:1 images are obtained. In this paper, we review the pertinent camera optics that set these nonnegotiable fundamentals and review a recently proposed method for focus distance estimation. We go beyond the original method descriptions to explain the mathematical justification for the PerspectiveX algorithm and provide an extension to profile images. This enables the first scientifically grounded use of profile view (or partial profile view) photographs in craniofacial superimposition. Proof of concept is provided by multiple worked examples of the focus distance estimation for frontal and profile view images of three of the authors at known focus distances. This innovation (1) removes longstanding trial-and-error components of present-day superimposition methods, (2) provides the first systematic and complete optical basis for image comparison in craniofacial superimposition, and (3) will enable anatomical comparison standards to be established from a valid grassroots basis where complexities of camera vantage point are removed as interfering factors.

Not so simple: Understanding the complexities of establishing identity for cases of unidentified human remains in an Australian medico-legal system

Discussions regarding the importance and complexities associated with the identification of deceased persons have typically focused on disaster or humanitarian contexts where there has been large scale loss of life. In contrast, identification efforts for unidentified human remains (UHR) cases in routine domestic casework contexts have received relatively little attention. The aim of this paper was to present the situation regarding the count of UHR cases in the state of Victoria, Australia, dating between 1960 and 2020, and to provide a constructively critical appraisal of the factors that have, and continue to, hinder their identification. Over the six decades a total of 132 coronial cases remained unidentified; an average of 2-3 cases per annum. For each case, the preservation of the remains, geographical location of where they were recovered from, primary (fingerprints, dental, DNA) and secondary identification methods that had been employed, potential for additional identification testing and current curation of the remains, were recorded. The difficulty with providing a "total count" of UHR cases is discussed, as well as the ways in which preservation, availability of identification methods, changes in policies and procedures, record management, changes in practice and advancements in technology, have impacted the identification process. This paper demonstrates the complexity of the investigation of UHR cases, and why individuals continue to remain unidentified in 2021.

Facial soft tissue thickness differences among different vertical facial patterns

In forensic facial approximation, facial soft tissue thickness (FSTT) measurements play a major role. These values are affected by many factors such as ethnicity, age and sex, in addition to measurement errors. We hypothesize that an additional source of error is the lack of consideration of facial type in the assessment of FSTT norms. The purpose of this study was to: 1- evaluate the presence of significant effects of vertical facial type within the FSTT measurements in adults and 2- assess the correlations between FSTT and hard and soft tissue cephalometric measurements. The sample consisted of the lateral cephalometric radiographs of 222 adult individuals (87 males; 135 females, 23.49±6.24 years of age) with normal occlusion and balanced profiles. Hard and soft tissue cephalometric measurements were taken, in addition to FSST at 10 facial landmarks. The sample was categorized into 3 vertical pattern groups based on the MP/SN angle: hypodivergent, normodivergent and hyperdivergent. Statistical analyses included MANOVA test and Pearson moment product for associations among variables. Statistically significant effect of vertical divergence on FSTT values was limited to the levels of Stomion, Labiomentale and Pogonion and FSTT measurements were associated with measurements related to the lower face (Lm and Pog) Moderate to high correlations between mandibular length and ramus length and FSTT values related to the lower face (LL, Lm and Pog mainly) emphasize further the important role of the underlying skeleton.

Craniofacial photographic superimposition: New developments

Craniofacial superimposition is a technique used in the field of forensic anthropology to assist in the analysis of an unknown skull. The process involves superimposing an image of the recovered skull over an ante mortem image of the suspected individual. In the past two decades, there has been a decline in the application due to the development of molecular analysis as a more precise and accurate identification technique. Despite its decrease in use, there has been significant development in superimposition techniques in the past five years, specifically to standardize procedures. One project, MEPROCS (The New Methodologies and Protocols of Forensic Identification by Craniofacial Superimposition), has attempted to establish a framework for solving the problems of past superimposition techniques. Future researchers should consider integrating information gleaned from clinical practices with the statistical and technical advances of craniofacial superimposition for better facilitating its use in forensic anthropology.

An overview of the latest developments in facial imaging

Facial imaging is a term used to describe methods that use facial images to assist or facilitate human identification. This pertains to two craniofacial identification procedures that use skulls and faces-facial approximation and photographic superimposition-as well as face-only methods for age progression/regression, the construction of facial graphics from eyewitness memory (including composites and artistic sketches), facial depiction, face mapping and newly emerging methods of molecular photofitting. Given the breadth of these facial imaging techniques, it is not surprising that a broad array of subject-matter experts participate in and/or contribute to the formulation and implementation of these methods (including forensic odontologists, forensic artists, police officers, electrical engineers, anatomists, geneticists, medical image specialists, psychologists, computer graphic programmers and software developers). As they are concerned with the physical characteristics of humans, each of these facial imaging areas also falls in the domain of physical anthropology, although not all of them have been traditionally regarded as such. This too offers useful opportunities to adapt established methods in one domain to others more traditionally held to be disciplines within physical anthropology (e.g. facial approximation, craniofacial superimposition and face photo-comparison). It is important to note that most facial imaging methods are not currently used for identification but serve to assist authorities in narrowing or directing investigations such that other, more potent, methods of identification can be used (e.g. DNA). Few, if any, facial imaging approaches can be considered honed end-stage scientific methods, with major opportunities for physical anthropologists to make meaningful contributions. Some facial imaging methods have considerably stronger scientific underpinnings than others (e.g. facial approximation versus face mapping), some currently lie entirely within the artistic sphere (facial depiction), and yet others are so aspirational that realistic capacity to obtain their aims has strongly been questioned despite highly advanced technical approaches (molecular photofitting). All this makes for a broad-ranging, dynamic and energetic field that is in a constant state of flux. This manuscript provides a theoretical snapshot of the purposes of these methods, the state of science as it pertains to them, and their latest research developments.

A history of forensic anthropology

Forensic anthropology represents a dynamic and rapidly evolving complex discipline within anthropology and forensic science. Academic roots extend back to early European anatomists but development coalesced in the Americas through high-profile court testimony, assemblage of documented collections and focused research. Formation of the anthropology section of the American Academy of Forensic Sciences in 1972, the American Board of Forensic Anthropology in 1977/1978 and other organizational advances provided important stimuli for progress. While early pioneers concentrated on analysis of skeletonized human remains, applications today have expanded to include complex methods of search and recovery, the biomechanics of trauma interpretation, isotopic analysis related to diet and region of origin, age estimation of the living and issues related to humanitarian and human rights investigations.

A discussion of current issues and concepts in the practice of skull-photo/craniofacial superimposition

A recent review paper on cranio-facial superimposition (CFS) stated that "there have been specific conceptual variances" from the original methods used in the practice of skull-photo superimposition, leading to poor results as far as accuracy is concerned. It was argued that the deviations in the practice of the technique have resulted in the reduced accuracies (for both failure to include and failure to exclude) that are noted in several recent studies. This paper aims to present the results from recent research to highlight the advancement of skull-photo/cranio-facial superimposition, and to discuss some of the issues raised regarding deviations from original techniques. The evolving methodology of CFS is clarified in context with the advancement of technology, forensic science and specifically within the field of forensic anthropology. Developments in the skull-photo/cranio-facial superimposition techniques have largely focused on testing reliability and accuracy objectively. Techniques now being employed by forensic anthropologists must conform to rigorous scientific testing and methodologies. Skull-photo/cranio-facial superimposition is constantly undergoing accuracy and repeatability testing which is in line with the principles of the scientific method and additionally allows for advancement in the field. Much of the research has indicated that CFS is useful in exclusion which is consistent with the concept of Popperian falsifiability - a hypothesis and experimental design which is falsifiable. As the hypothesis is disproved or falsified, another evolves to replace it and explain the new observations. Current and future studies employing different methods to test the accuracy and reliability of skull-photo/cranio-facial superimposition will enable researchers to establish the contribution the technique can have for identification purposes.