Cephalometric landmark location uncertainty: this is related to the extremely difficult task of locating the points in a completely reproducible manner. The variability may arise from reasons such as:
a) Variation in the distribution of shadows that are dependent on lighting condition during photography.
b) Unsuitable camera focusing, especially when the plane of focus is too shallow and hence the critical features are not sharp.
c) Poor image quality. i.e. low resolution.
d) Face posture in the photograph, i.e. facial expression and angle of view of the face (lateral, frontal or oblique).
e) Landmark occlusion due to the presence of elements such as hair or glasses.
f) Imprecise definition of some anthropometric landmark, could be either due to ambiguous terminology or because it is poorly defined in an anatomical sense.
Landmark matching uncertainty: refers to the imprecision that is involved in the matching of two sets of potentially corresponding landmarks derived from two different objects, a face and a skull.
a) The correspondence between facial and cranial anthropometric landmarks is not always symmetrical and perpendicular to the skin surface and to the underlying bone.
b) The facial soft tissue depth varies for each cephalometric landmark, as well as for different populations (based on age, race, and sex).
c) Considerations of how the distances between potentially corresponding landmarks are affected by the posture and facial expression in the image have to be taken into account.
d) There are many studies describing the uncertainty related to differing soft tissue depths for different populations but almost none of them considered the projection of those distances onto the AM photo used in the comparison.
Skull-face overlay uncertainty: there is no precisely quantifiable way of determining when an accurate superimposition has been achieved.
There are many unknown (and/or uncertain) parameters involved in the replication of the original photographic conditions used to produce the image employed in the comparison.
Morphological criteria are subjective or difficult to quantify.
The amount of morphological criteria that have to be satisfied for a positive identification.
The effects of dental changes detected from examination of the AM photographs used for comparison with the skull, as well as their accurate interpretation.
Age related changes in the craniofacial morphology children need to be investigated and documented more comprehensively before comparisons between images taken at different times during childhood can be compared.
The following “best practices” and “practices that should be avoided” represent some guidelines to minimize or avoid the main sources of error, as well as, to deal with the sources of uncertainty that are concomitant to the application of CFS.
These steps should be viewed as recommendations and under no circumstances should they be perceived as requirements to accomplish a "valid" result. The authors are fully aware that the circumstances of each case are to be taken into consideration, when evaluating the results of an identification based on craniofacial superimposition.