• Sergio Damas
  • Oscar Cordón
  • Oscar Ibáñez
Open Access


The conclusions of this handbook cannot be separated from the MEPROCS project where the manuscript was first conceived and then progressively developed by the team through a wide variety of tasks contributing to the final document.

10.1 Introduction

The conclusions of this handbook cannot be separated from the MEPROCS project where the manuscript was first conceived and then progressively developed by the team through a wide variety of tasks contributing to the final document.

It is not a trivial task to summarize the main points resulting from 30 months of difficult work at an international level. Beyond the particular conclusions that are detailed below, the main global achievement of the MEPROCS project is the focus toward an international standard in craniofacial superimposition. To the best of our knowledge, such standardization has never been attempted before in the field of forensic anthropology. Furthermore, the particular standardization approach followed in MEPROCS and described in this handbook can be easily replicated in some other forensic disciplines where similar initiatives are demanded.

The absence of similar joint efforts in the past or at least the lack of public documentation represented a real challenge for MEPROCS. This handbook is a first attempt to resolve the situation and facilitate similar works in the future.

In this chapter, the main achievements of the MEPROCS project are presented in Sect. 10.2. Sect. 10.3 describes the problems encountered during the project and the way they were solved. Section 10.4 is devoted to present some future works and research proposals. Finally, some concluding remarks are included in Sect. 10.5.

10.2 Main Achievements

When compared to what the state of the art was before MEPROCS, there are plenty of important achievements that are directly related to the tasks performed in the project. Some of the most representative are enumerated as follows:

  • The handbook. This represents one of the most important achievements of the project. From the very beginning, when the MEPROCS proposal was formulated and submitted for evaluation to the European Commission, it was our intention to achieve an international agreement with practical use. This was a twofold challenge: the contents and its distribution. The former was a challenge, because the standardization task had not been tried before in the field. The distribution was also challenging as we wanted to facilitate as much as possible global access to the handbook. The publication in an open-access format by Springer (one of the leading publishing companies in the world) solved this issue.

  • Global effort. One of the most important MEPROCS characteristics was the aim to be a global initiative. It was global because for the first time there was a collective, interdisciplinary, and international effort focusing on craniofacial superimposition. Furthermore, it was open and inclusive so that new institutions interested in this technique could join the project at any time. The conclusions of the project would be more important for the evolution of the technique and the profession in general, if the final number of participants was greater than the initial consortium. In particular, the number of institutions involved in MEPROCS evolved from the starting 7 institutions up to more than 30. At the moment, most of the participant institutions are willing to continue in collaboration to achieve the pending MEPROCS objectives together with any other task that could contribute to the evolution of the technique beyond the time constraints imposed by the commitments related to a project using public funds.

  • Global analysis. For the first time, the technique was analyzed considering the different tasks involved along the whole process of craniofacial superimposition, that is, from the very first steps to study the skull found (once cleaned) to the final report. This type of analysis may be considered global in its approach.

  • Global participants. MEPROCS attracted the attention of a broad variety of end-users, that is, professionals who have important responsibilities in forensic identification. In particular, both researchers and practitioners were crucial to achieve the MEPROCS objectives. Among them, we emphasize the collaboration of the police forces of four different countries. Furthermore, the role of the technical institutions that joined MEPROCS was equally important and the need for a multidisciplinary team to properly approach the CFS technique was demonstrated.

  • Common data. In order to achieve international agreements that lead to standards on CFS, it was vital to avoid the bias induced by the subjective evaluations of the results. That was only possible with a purely objective approach to all the MEPROCS tasks based on the study of the same data. Important legal and ethical issues were analyzed and addressed in order to share the data among the MEPROCS participants worldwide. Finally, we would like to thank the data providers for their altruistic and crucial contribution to the success of the project. In particular, Prof. Caroline Wilkinson (University of Dundee) who provided the data with the permission of the University of Tennessee, Dr. Fabio Cavalli (Azienda Ospedaliero-Universitaria di Trieste) who provided clinical data, Dr. Cristina Cattaneo (University of Milan), and Dr. Rimantas Jankaukas (Vilnius University) who provided data from their own laboratories.

  • Ground truth. Unlike some other more established forensic techniques, there was a lack of ground-truth data in craniofacial superimposition, that is, a procedure that could provide a perfect skull-face overlay in an objective and unquestionable manner. This information is fundamental for the appropriate validation of any technique. MEPROCS provided the first ground-truth dataset for craniofacial superimposition. Only with the availability of such ground-truth data, the most relevant criteria to analyze a particular superimposition could be recommended.

  • Specialized training. The International Conference on Craniofacial Superimposition (ICCFS-2014) took place in Dundee in July 2014. It was the final and most important MEPROCS event and the first international conference specifically devoted to craniofacial superimposition. The ICCFS-2014 technical program was rich and varied, including two keynote speakers renowned worldwide. During the last 3 days of the conference, the delegates (more than 100) had a unique opportunity to receive a diverse and high-quality training on craniofacial superimposition based on the MEPROCS recommendations and including the approaches of different laboratories from all around the world.

  • First standard in the field. The aim of the first technical study performed in MEPROCS was to assess the reliability of different craniofacial superimposition methodologies and the corresponding technical approaches to this type of identification. With all the data generated, some of the most representative experts in craniofacial identification joined in a discussion intended to identify and agree on the most important issues to be considered for craniofacial superimposition. As a consequence, the consortium produced the first standards in the field, including best and worst practices, sources of error and uncertainties, technological requirements and desirable features, and, finally, a common scale for the craniofacial matching.

  • Set of evaluation criteria. The purpose of the second technical study was to analyze the subjectivity and discriminative power of the different criteria for assessing the skull-face correspondence as proposed in the literature or by any of the MEPROCS partners. This novel study provided important insights to better understand: (1) which are the most and less discriminative criteria; (2) which criterion depends more on the expert who is evaluating it and which criteria are more independent, that is, less subjective. Even though the conclusions drawn in the study were influenced by the materials employed (i.e., cone-beam CTs [CBCTs] that lacked the upper part of the skull and presented additional inconveniences), the proposed methodology was itself a great achievement that may lead to further and more thorough studies.

  • MEPROCS framework. According to the conclusions of the two technical studies, the MEPROCS consortium defined the MEPROCS framework to aid in the application of craniofacial superimposition. The framework consists of best and worst practices, sources of error and uncertainties, technological requirements and desirable features, a common scale for the craniofacial matching evaluation, and finally a set of evaluation criteria. See Chap.  8 for a detailed description of the framework.

  • Performance evolution analysis. Once the craniofacial superimposition framework was proposed, a third technical study was performed. All partners were asked to deal with a variable number of CFS cases (positives and negatives) following all the recommendations collected within the framework. Individual and average performance was compared with the performance achieved during the first study in order to analyze its evolution (either positive or negative) when considering the MEPROCS framework. Though the number of participants was limited, the performance of the majority improved when they followed the MEPROCS recommendations.

  • International awareness. Craniofacial superimposition, although existing for at least a century, is still a controversial technique within the scientific community. That is demonstrated by the small number of recent publications. The evolution of the use of craniofacial superimposition strongly depended on the specific country and the frequency of potential cases as well as the available means to apply alternative identification techniques. In developed countries, the small number of cases and the recent advances in alternative and more expensive techniques for identification led to a progressive reduction in the application of craniofacial superimposition. In contrast, the large number of cases in developing countries is typically related to high criminal rates or humanitarian issues such as crimes against humanity or identification following mass disasters. Also, the funds for identification are usually limited in these regions. This situation leads to a very frequent application of the technique in such countries. MEPROCS faced this duality and the need to awaken interest on the international consolidation of the technique. In particular, different labs have shown a new interest in craniofacial superimposition. MEPROCS has also laid the foundations for a more reliable technique. Definitely, the advances in the reliability of the technique will involve a broad number of new stakeholders.

  • From experts’ opinions to studies of metadata. In craniofacial superimposition, as in forensic identification in general, both legal authorities and the scientific community are insisting upon real science in forensic identification, that requires the successful demonstration of individualization (i.e., an expert’s confirmation of a particular set of characteristics unique to the deceased (Holobinko 2012). The core assumptions that underpin conventional forensic craniofacial superimposition rely more on experience and faith than on empirical evidence. Perception and judgment may be affected by bias, expectations, beliefs, and motivations. Many forensic disciplines, including identification sciences like anthropology, involve some degree of subjectivity. Disciplines like forensic anthropology may be problematic to the courts since they may sometimes employ a combination of traditional scientific methodologies and less rigorous observational methodologies coupled with case study evaluations or casework experience. Since the 1993 US Daubert ruling, many forensic disciplines including anthropology have determined that there is a need to critically reevaluate some of the techniques and methods used in their examinations, as well as the validity of the underlying scientific theories (Christensen and Crowder 2009; Saks 2010). It is therefore imperative to minimize the risk of error through quality assurance (i.e., proper training, method validation, accreditation, and certification). Quality assurance in forensic anthropology can be established through validation studies of analytical methods in order to determine method reliability (precision and accuracy) and through the development of professional standards in the form of best practice protocols. Subjectivity is not necessarily equal to unreliability (Christensen and Crowder 2009); thus, nothing is preventing at least some types of anthropological testimony from being admitted as technical expert testimony under the Kumho standard, as the court acknowledges that science is too complex to evaluate with a single set of standards (Grivas and Komar 2008). The potential users of practical guidelines, other recommendations, and protocols need to know how much confidence they can place in such recommendations. Protocols must be systematically developed by panels of experts with access to the available evidence, an understanding of the problem and research methods, and sufficient time for reflection (Grade-Working-Group 2004) that the MEPROCS project provided. Some of the key elements of the methodology discussed in these guidelines are the fact that they were developed by a multidisciplinary group; they were based on a systematic review of the scientific evidence; and recommendations were linked to the supporting evidence and graded according to the strength of that evidence.

10.3 Problems Encountered

It is important to highlight that the achievements were reached after solving some problems encountered. The problems presented threats for the success of the project, but they were addressed in the following ways:

  • Ethical and legal issues to share data. Important legal and ethical issues were analyzed and addressed in order to share the data among the MEPROCS participants world-wide. In particular, two different forms were distributed to every data provider and data user. In the first form, the data provider certified the data release for scientific purposes, according to his national laws and ethical regulations/ethical committee/etc. This included a number of cases consisting of either ante-mortem photographs, laser-scans of the skull, x-rays of the skull, CTs of the skull, or any other. The data provider also certified that for the cases provided, the person had been positively identified via DNA/dental records/other. In the second form, the user was informed about the kind of material provided and the particular terms of use of such material. The user certified that he was the scientific lead from his institution for the MEPROCS project. Also, he certified that he could receive the scientific material for scientific purposes and accepted the previous terms of use and all the applicable regulations according to his national laws and ethical regulations, ethical committees, etc. The particular templates of both forms can be found in Appendix C.

  • Technical issues to obtain ground-truth data. The precise projection of the skull onto a photograph of the same person is not a trivial task. After thorough analysis of the problem, the MEPROCS participants determined that the only chance to achieve it was using clinical data (which also involved an informed consent that the patient should sign to facilitate the data use). The particular procedure to obtain the ground truth included images resulting from orthostatic Cone-Beam CT processed to obtain the corresponding 3D face and 3D skull models. After positioning homologous points in both the 3D face model and the photograph of the patient, the former was automatically projected onto the latter to produce a perfect match. Then, the parameters were applied to the 3D skull model, resulting in a perfect SFO. The latter superimposition is considered a ground-truth skull-face overlay. A detailed explanation is given in Ibáñez et al. (2015).

  • Coordination difficulties. It was challenging to coordinate a large group of very renowned experts, researchers, and practitioners with different experiences and interests. The use of the technique is marginal in some countries, while it plays a crucial role in others. In order to overcome these difficulties, MEPROCS was always guided by the global aim to perform a scientific and objective approach to every single task of the project. In this sense, the role of the technical studies was essential. Also, the tireless efforts to reach global agreements that were only possible in face-to-face meetings should be emphasized.

  • Economic limitations. Initially, the MEPROCS consortium consisted of seven partners. The project activities and their corresponding budget were scaled according to this size. Though one of the objectives of the project was to involve new institutions, we did not expect the positive and proactive attitude of so many additional participants. This represented a great opportunity for international collaboration (which was the main aim of the project), but, at the same time, we had to properly manage our limited funds. We requested some modifications in the budget from the project officer in Brussels in order to respond to this new situation. The total amount of funds remained the same, but we proposed some changes among different items of the budget. Once approved by the European authorities, we could use the funds to organize six meetings (attended by 20 persons, average), one international workshop (attended by 30 delegates), and the final conference that supported the travel and accommodation expenses (together with bursaries for students) of more than 80 delegates.

  • Time constraints. Initially, the MEPROCS duration was 24 months. The appropriate use of the original MEPROCS grant to support the activities of many more new institutions was not easy. Beyond that economical challenge, the involvement and active collaboration of an important number of new participants had an important impact on the MEPROCS schedule as well. The project became more ambitious because it was a great opportunity to launch new technical studies that were not originally planned. This situation was explained to the European authorities who approved the extension of the project for six additional months, considering the same funds initially granted for the project. Throughout this period of time (30 months) and until the very last day, there was continuous work in the numerous tasks of the project with a special effort on the handbook.

10.4 Future Trends and Research Propositions

The diverse support received by the forensic community, together with the different interests and uses of the technique in different countries, and the significant differences obtained in the reliability studies developed so far lead us to identify three main challenges in craniofacial superimposition for the future:

  • The need of a broader study on the evaluation criteria. MEPROCS suffered a limitation as far as the resources and materials employed to analyze the subjectivity and discriminative power of the different criteria for assessing the skull-face correspondence are concerned. This is a crucial aspect that deserves important attention in the future. The methodology followed in MEPROCS should lead to further studies involving significant numbers of participants evaluating a relevant number of cases. Some of the aims of such studies should be the selection of the more significant criteria and the connection of the criteria with the decision degrees included in the MEPROCS framework, that is, the estimation of the criteria that should be satisfied to support every decision degree.

  • The need of objective assessment and automation. Knowledge exchange and the possibility to improve existing approaches and propose new methods to solve problems are the main forces behind the evolution of science. The guarantee of objective procedures to evaluate the performance of those proposals is essential.

To compare the performance of newly developed CFS methods, a common forensic dataset of known case studies should be available. In this way, the validation of the methods proposed could be applied to solved cases and thus comparison of the results with the identification previously determined by forensic anthropologists.

The absence of a common repository of solved CFS cases has limited the development of automatic methods that could solve some of the most tedious CFS tasks in a fast, accurate, reproducible, and objective way. To date, few automatic CFS tasks are used in practical applications despite the high number of cases examined and the large amount of time that the forensic expert spends in performing the examination. In particular, skull-face overlay was as a very challenging and time-consuming part of the craniofacial superimposition technique. Despite the existence of promising works in this direction, automatic techniques have not been implemented on a large scale due to the inability to test their performance in an objective manner.

It is thus essential to obtain ground-truth data and there are a number of open problems related to use of Cone-Beam CTs (CBCTs). Since CBCTs are employed for maxillofacial treatments, the images’ acquisition field generally lacks the upper part of the head because it is useless for those purposes. Moreover, the inclusion of the upper part of the head would represent a needless additional radiation of the patient. Nevertheless, that lack of information is a clear limitation for many craniofacial superimposition tasks. In particular, this is an important shortcoming for the appropriate evaluation of the results. Furthermore, the segmentation of the available CBCT data to obtain only the bonny part of the whole medical image is another real challenge. There are plenty of artifacts typically from tooth fillings that really complicate this task. Also, CBCTs’ resolution is not as good as conventional CTs, which were discarded in MEPROCS ground-truth studies (Ibáñez et al. 2015), because the gravity could have an impact on the flesh that would invalidate the potential conclusions drawn from such data.

  • The need of a significantly large reliability study. Such a reliability study should take into consideration the two previous points. On the one hand, this crucial task was not faced in MEPROCS due to the lack of time. Therefore, the statistical basis for the use of the technique has not been produced by the studies conducted in MEPROCS. On the other hand, the reliability studies reported in the literature are fraught with limitations. The absence of an objective measure of the skull face overlay match, technical limitations of the equipment, disregard for accurate landmarks location while performing landmark based methods, absence of soft tissue data for the tested population, insufficient quality of the 3D cranial models, postmortem photographs, reduced samples, absence of appropriate statistical analysis, and the absence of inter- and intraobserver studies are just a few of such shortcomings. Statistically significant reliability studies that tackle the challenges identified in this manuscript are required to obtain a more solid picture on the reliability of craniofacial superimposition and its potential complementary role with other forensic sciences techniques.

10.5 Concluding Remarks

Most of the aforementioned future trends and research propositions can only be properly faced by a multidisciplinary team. After MEPROCS, we can conclude that many of the achievements were only possible thanks to the diverse consortium that consisted of forensic laboratories, police forces, and technical institutions. In particular, the application of craniofacial superimposition requires an awareness of the technical implications related to imagery, discipline that is in continuous and fast technological development, especially with regard to three-dimensional images and interactivity. This technological trend may lead, in the near future, to new and more sophisticated imaging tools. These new tools will need to be carefully evaluated from time to time for their potential use in craniofacial superimposition.

Objective and unbiased validation studies over a significant number of cases are required to get a more solid picture on craniofacial superimposition reliability. It will not be possible to compare the performance of existing and upcoming methods for craniofacial superimposition without a common forensic database available for the research community. Skull-face overlay is a key task within craniofacial superimposition that has a direct influence on the subsequent task devoted to evaluate the skull-face relationships. Once legal and ethical issues are overcome to facilitate the public use, the creation of a database of skull-face overlay cases is a real need.

Besides, new statistical and computational techniques should be devised based on the available data. Soft computing and computer vision should play an irreplaceable role in the evolution of the technique.

In general, we can’t confirm that the current state of the technique is mature enough to be used as sole evidence for positive identification; however, we can confirm that those who follow the MEPROCS recommendations greatly improve their performance and have a better scientific basis.


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Authors and Affiliations

  • Sergio Damas
    • 1
  • Oscar Cordón
    • 1
  • Oscar Ibáñez
    • 2
  1. 1.Edificio de InvestigaciónEuropean Centre for Soft ComputingMieresSpain
  2. 2.Department of Computer Science & Artificial Intelligence (DECSAI)University of GranadaGranadaSpain

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