Identifying a steganographer in realistic and heterogeneous data sets
Andrew D. Ker, Tomáš Pevný · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2012
We consider the problem of universal pooled steganalysis, in which we aim to identify a steganographer who sends many images (some of them innocent) in a network of many other innocent users. The detector must deal with multiple users and multiple images per user, and particularly the differences between cover sources used by different users. Despite being posed for five years, this problem has only previously been addressed by our 2011 paper. We extend our prior work in two ways. First, we present experiments in a new, highly realistic, domain: up to 4000 actors each transmitting up to 200 images, real-world data downloaded from a social networking site. Second, we replace hierarchical clustering by the method called local outlier factor (LOF), giving greater accuracy of detection, and allowing a guilty actor sending moderate payloads to be detected, even amongst thousands of other actors sending hundreds of thousands of images.