Heightened international concerns relating to security and identity management have led to an increased interest in security applications, such as face recognition and baggage and passenger screening at airports. A common feature of many of these technologies is that a human operator is presented with an image and asked to decide whether the passenger or baggage corresponds to a person or item of interest. The human operator is a critical component in the performance of the system and it is of considerable interest to not only better understand the performance of human operators on such tasks, but to also design systems with a human operator in mind. This paper discusses a number of human factors issues which will have an impact on human operator performance in the operational environment, as well as highlighting the variables which must be considered when evaluating the performance of these technologies in scenario or operational trials based on Defence Science and Technology Organisation’s experience in such testing.