Before analyzing the images themselves, we looked at the geographical context of their display.  Many students in the class had never been to New York City or seen the Trade Center towers in person.  This field context of the missing persons posters was emphasized by a team of geographers from Rutgers:
 

Posters proved to be a rich source of information about many human dimensions of disaster. Among others, they provided insights about: the disaster-impacted population; the role of vernacular information and "grass roots"  contributions to formal systems of disaster management; informal information display and communication strategies; the multiplicity of messages about hazard that are contained in everyday urban landscapes as well as crisis ones; and differential neighborhood responses to disaster.   (Mitchell)

The urban context and the particular kairos of New York City after the disaster was not information that was immediately accessible to my students.  They responded to the images from missing persons posters and analyzed them without a sense of nearby images or landmarks.