Skull-face overlay and, in particular, the adequate perspective of the skull. For example, most of the software programs employed for this task do not allow alteration of the projection, but “just” the orientation and scaling. In many cases it involves an error-prone trial and error process. Orientation + scaling + perspective.
The digital articulation of the mandible and cranium after scanning can introduce errors. With no access to the occlusion as it was in life, the mandible may have been placed in an incorrect position with respect to the cranium.
The attachment of the mandible to the cranium.
The replication of the AM position of the mandible.
The incomplete preservation and postmortem reassembly of the skull. For example, the incorrect positioning of teeth in the sockets.
The inaccurate 3D skull acquisition (or segmentation in case of CT scanner), precision below <1mm and/or specific features not properly scanned (or segmented). The latter was recorded at the nasal region, the teeth and the orbits. Presence of artefacts.
The aspect ratio of the photograph (the ratio between horizontal and vertical sizes of the image).
The unknown origin of the AM photograph, i.e., when the AM photograph is not the original one acquired by a digital camera (original digital file) or an analogic one (original revealed photography).
The post-mortem skull damage.
All the above issues are considered sources of errors, thus, they should be considered in order to avoid accumulating and propagating errors during the CFS process. In addition, there are several issues that can negatively affect conclusions based on CFS but, unlike sources of errors, they cannot be avoided. In contrast, they have to be considered an inherent part of the process, and thus, they have to be properly modelled and incorporated in the decision making process. Unlike complete and precise knowledge, the latter issues represent partial, incomplete, imprecise and/or vague information. We thus referred to them as sources of uncertainty.