Digital Evidence
OSAC’s Digital Evidence Subcommittee focuses on standards and guidelines related to information of probative value that is stored or transmitted in binary form. As of October 2023, this subcommittee has had five standards placed on the OSAC Registry. Of these standards, three have been developed through ASTM International, an SDO with engagement in many industries that, prior to its involvement in forensics, has a long history of acceptance by the legal system. Two other standards have been developed through the Scientific Working Group on Digital Evidence (SWGDE), which currently operates as an SDO for digital evidence.
ASTM E3017-19, Standard Practice for Examining Magnetic Card Readers, is a good example of a digital standard for this subcommittee and illustrates some of the types of information included in standards that can aid courts in dealing with technology. This standard lays out how examiners should seize, acquire, and analyze data from magnetic card readers, known as skimmers when used unlawfully. These examinations can reveal (or equally fail to reveal) evidence of “unauthorized” (i.e., stolen) information and so can play an important role in defending or prosecuting criminal cases.
Within this standard, courts can find explanations of important terminology, information about collection techniques and data analysis, and some discussion of the technique’s limitations, among others, all of which can aid courts when considering the examination of skimming devices. As the standard itself states, its application “cannot replace knowledge, skills, or abilities acquired through education, training, and experience.” This standard, and others developed and promoted by this subcommittee, can give judges a place to begin their understanding of digital evidence and where and how it fits into the proceedings in their courtroom. For example, a court in a jurisdiction where standards on the OSAC Registry have been implemented might expect to hear testimony about this standard when skimming cases are heard; in those circumstances, a judge deciding admissibility (or sitting as a fact-finder) might consider how the evidence being offered comports with, or fails to comport with, the standard. Even where this standard is not raised by litigants or is otherwise unavailable to be considered directly by the court, a preexisting familiarity with the standard would nonetheless aid the court in understanding the evidence being offered.
Facial & Iris Identification
OSAC’s Facial & Iris Identification Subcommittee focuses on standards and guidelines related to the image-based comparisons of human facial and iris features. As of October 2023, this subcommittee has nine standards on the OSAC Registry, including a joint standard detailed below. Five of those standards are OSAC Proposed Standards, which are also currently with ASTM International and working through the ASTM standards development process. While facial identification is often highly technical, the standards currently on the OSAC Registry reflect the broader scope of facial identification practice, including facial comparison, which is “a manual process conducted by a human which entails identifying similarities and differences between two images or an image and a live subject to determine whether they represent the same person.”
One important OSAC Proposed Standard that is currently under development at ASTM International is OSAC 2022-S-0007, Standard Guide for Facial Comparison: Overview and Methodology Guidelines. While this OSAC Proposed Standard is being finalized at ASTM and is still subject to change, OSAC encourages its adoption while the SDO process continues. Our belief is that OSAC Proposed Standards that have completed the development and review process at the OSAC level are sound interim documents that should be available to and considered for implementation by the forensic science community.
ANSI/ASTM E3149-18, Standard Guide for Facial Image Comparison Feature List for Morphological Analysis, currently on the OSAC Registry, details a “set of facial components, characteristics, and descriptors” that should be used during facial comparisons using morphological analysis, the recommended method for manual facial comparison. This standard, read together with OSAC 2022-S-0007, Standard Guide for Facial Comparison: Overview and Methodology Guidelines, represents the ongoing nature of standards going through OSAC’s Registry approval process. No subcommittee has or will have “complete standards” that cover every aspect of a forensic science discipline. Not only does the science on which digital evidence rests constantly grow and change, but as OSAC’s work continues, these standards will build on each other over time.
In addition to these standards, two more of the Facial & Iris Identification Subcommittee’s standards deal with how facial images for comparison should be taken for both living and deceased subjects.
Speaker Recognition
OSAC’s Speaker Recognition Subcommittee focuses on standards and guidelines related to the practice of speaker recognition, voice data collection, measurement, transmission, and retrieval. The Speaker Recognition Subcommittee currently has one standard on the OSAC Registry, AES76-2022: AES Standard for Audio Forensics—Speech Collection Guidelines for Speaker Recognition: Interviewing at a Temporary Location. This document explains how known speaker samples to be used in a later speaker-recognition process should be collected in nonlaboratory locations. This subcommittee also has a number of important documents under development, including a validation standard for forensic speaker recognition.
Outside of its standards drafting efforts, the Speaker Recognition Subcommittee has also produced a “process map,” which is a graphical representation of the discipline’s current practices. This process map shows in detail the decisions examiners in this field make at different junctures and some of the varying paths examinations might take. This document can help courts understand the current approaches in the speaker recognition discipline.
Video/Imaging Technology & Analysis (VITAL) Subcommittee
OSAC’s VITAL Subcommittee works on standards and guidelines related to the application of methods and technologies to analyze information related to forensic imagery from a variety of systems. The impact this discipline has across the forensic space is seen in the variety of its documents, both in the SDO published and OSAC Proposed Standards that are on the OSAC Registry. For example, one VITAL standard on the OSAC Registry is ANSI/ASTM E3235-21, Standard Practice for Latent Print Evidence Imaging Resolution. This standard provides recommendations on the level of resolution necessary for latent print imagining systems and equipment to enable fingerprint examiners to make appropriate comparisons. Such a cross-disciplinary effort reveals the importance of technology, not only to digital forensics but also to traditional forensic techniques. VITAL has also shared its work on standards with the Facial & Iris Identification Subcommittee. Together, these subcommittees have collaborated on several OSAC Proposed Standards listed on the OSAC Registry—one addressing post-mortem photography and another entitled OSAC 2022-S-0001, Standard Guide for Image Comparison Opinions (see below).
Interdisciplinary Standards
An advantage of OSAC’s structure and its use of various SDOs is that, in addition to discipline-specific standards, standards that span multiple disciplines can be drafted and placed on the OSAC Registry. These interdisciplinary standards can be of importance in rapidly changing technological environments. One such standard is ASTM E2916-19, Standard Terminology for Digital and Multimedia Evidence Examination, which “is a compilation of terms and corresponding definitions used in the examination of digital and multimedia evidence to include the areas of computer forensics, image analysis, video analysis, forensic audio, and facial identification.” An interdisciplinary standard such as this can help ensure that experts and courts are speaking (and understanding) the same language.
Another critical interdisciplinary standard is OSAC 2022-S-0001, Standard Guide for Image Comparison Opinions, which involves collaborations between members of OSAC’s VITAL and Facial & Iris Identification Subcommittees. This OSAC Proposed Standard, currently included on the OSAC Registry and at ASTM International for further development, aims to “increase harmonization and consistency by providing a framework of opinion categories across and within the digital multimedia forensic disciplines that compare images.” The OSAC Proposed Standard directs disciplines involved in image comparisons to use this standard when developing and validating discipline-specific opinion categories and to reference “any empirical studies of the scale for opinions about the weight of evidence for the applicable type and quality of evidence.” Importantly, the standard states that, currently, few “standardized opinion scales with associated validation data . . . exist.” The standard goes on to require opinion scales produced to this standard to “explicitly state” when that is the case, i.e., when no relevant validity studies exist. This standard is of great value to a judiciary and a legal system trying to grapple with how to appropriately understand and weigh forensic evidence.
Other Resources
Several other materials exist that can aid courts in understanding the standards of the OSAC Registry. Under a cooperative agreement with NIST, the American Academy of Forensic Sciences (AAFS) has produced fact sheets, which are one-page documents intended to summarize standards in clear and easy-to-understand language. Fact sheets are available for most standards on the Registry and can be accessed by a hyperlink that is under the standard on the OSAC Registry webpage. These documents can serve as a useful launch point for courts in understanding what a standard means and how it fits into a broader forensic practice. It should be noted that these fact sheets are not intended to serve as definitive interpretations of the standards and are not produced by NIST.
Courts in the process of undertaking general education about standards may also be interested in the list of available research and development (R&D) needs produced by each subcommittee. These R&D needs describe specific gaps in the knowledge base and can be used to support the drafting and refinement of standards as well as to draw in research to help fill those gaps to provide a stronger scientific foundation. These assessments also include bibliographic references and explanations for why this research is necessary. For example, in 2021, the VITAL Subcommittee’s Research Needs Assessment for Detecting Deepfakes identified that there was a major gap in the current knowledge and that there was no or limited research being conducted on this important problem, which could, per the subcommittee, result in “geopolitical, criminal implications, or civil unrest.” Since its posting, there has been significant research performed in this area, both in forensic science and in the broader scientific community. These documents illustrate what some of the most experienced and active practitioners in a field view as the state of their science and their efforts to steer researchers into working on these important areas to assist with these challenges, and, to that end, can serve to educate judges about where research may be most needed in particular fields.
Other Technological Standards
Technological advances in forensic science are not limited to digital evidence, and the standards on the OSAC Registry reflect that. For example, DNA analysis has undergone significant changes since its first usage, and now many laboratories and FSSPs use computer-based probabilistic genotyping systems to “infer genotypes and/or calculate likelihood ratios.” One important standard on the OSAC Registry is ANSI/ASB Standard 018, Standard for Validation of Probabilistic Genotyping Systems, which lays out what a practitioner must do to validate their lab’s system. The future technologies being brought online to support the examination of firearms are also addressed with standards. There are three standards on the OSAC Registry that provide guidance for implementing new 3D measurement systems for enhancing the traditional 2D method of firearms analysis and comparisons. Over time, these standards will help guide laboratories on how to implement these new technologies into their operations following a technically sound approach. As technology continues to shape forensic practice, so, too, will the standards on the OSAC Registry reflect those changes in various disciplines.
A Note on Human Factors Both in OSAC and Beyond
Even the most technologically advanced forensic technique is, at its core, a human endeavor and can be subject to error. The structure of OSAC implicitly recognizes this, and one of the task groups that serves as a resource to the various committees is the Human Factors Task Group. Human factors broadly “examine[ ] the interactions between humans and other elements of a system—technology, training, decisions, products, procedures, workspaces, and the overall environment—with the goal of improving both human and system performance.” Accordingly, the Human Factors Task Group is made up of people chosen for their “experience in psychology, cognitive science or a related social science discipline, and knowledge of social science literature on human judgment, decision making, observer effects, communication and cognitive bias.” This expertise is used to help the various subcommittees draft standards that appropriately address the wide range of human factors that can affect the outcome of forensic examinations.
Outside of OSAC, NIST has been engaged in other efforts to promote a fuller understanding of human factors in forensic analysis. For example, NIST has published two Expert Working Group Reports on human factors topics—one on latent fingerprint examination and one on handwriting analysis. A third report is forthcoming on human factors in DNA analysis. These reports represent an important contribution to the scientific understanding of human factors in forensic science, and courts may find them a useful entry point into this field of study.
Conclusion
Forensic science and the technologies that support it can be intimidating, but it does not have to be. NIST’s work in forensic science standards, through OSAC and other efforts, can help foster not only better science within labs but also a more fulsome understanding of science in courtrooms. OSAC’s work can be an important guide to the judiciary in its efforts to ensure its use of science is consistent with the goals of justice and fairness for those who come before it.