Methods and apparatus for detecting a composition of an audience of an information presenting device are disclosed. One disclosed method captures images of the audience, determines a number of people within the images and prompts the audience to identify its members if a change in the number of people in the audience is visually detected. This disclosed method avoids both under sampling of the audience and excessive prompting of the audience by only requesting entry of identification data when an audience change occurs. Methods and apparatus to determine the number of persons in an image or series of image are also disclosed.