Use of data to inform expert evaluative opinion in the comparison of hand images-the importance of scars.

Evaluation of a likelihood ratio is widely recognised as the most logical and appropriate means of assessing and expressing the weight of expert scientific evidence. This paper describes the application of such an approach to cases involving the comparison of images of hands that contain visible scars. Such evidence is frequently provided in cases of alleged child sexual abuse in which images of the perpetrator's hand are compared with images of the suspect/accused's hand. We illustrate how data provided from a database of hand images can be used to inform the probabilities that are an essential part of evaluating a likelihood ratio and, hence, how data have a bearing on the appraisal of the weight of evidence that can be attributed when scars are present within an image.