1. A face image tracking system for a site, comprising: a data storage; an imaging device; a display; and a processor configured to: store, in the data storage, face images of persons that were acquired when the persons visited the site, tag one or more of the face images stored in the data storage, obtain a face image of a person that is captured by the imaging device in response to a request to delete a face image of the person stored in the data storage, extract one or more stored face images that have at least a threshold similarity to the face image of the person captured by the imaging device, delete one of the extracted face images from the data storage when said one of the extracted face images is not tagged, and display, on the display, information indicating that said one of the extracted face images cannot be deleted when said one of the extracted face images is tagged.