Steganalysis of LSB replacement using parity-aware features

Abstract

Detection of LSB replacement in digital images has received quite a bit of attention in the past ten years. In particular, structural detectors together with variants of Weighted Stego-image (WS) analysis have materialized as the most accurate. In this paper, we show that further surprisingly significant improvement is possible with machine-learning based detectors utilizing co-occurrences of neighboring noise residuals as features. Such features can leverage dependencies among adjacent residual samples in contrast to the WS detector, which implicitly assumes that the residuals are mutually independent. Further improvement is achieved by adapting the features for detection of LSB replacement by making them aware of pixel parity. To this end, we introduce two key novel concepts - calibration by parity and parity-aware residuals. It is shown that, at least for a known cover source when a binary classifier can be built, its accuracy is markedly better in comparison with the best structural and WS detectors in both uncompressed images and in decompressed JPEGs. This improvement is especially significant for very small change rates. A simple feature selection algorithm is used to obtain interesting insight that reveals potentially novel directions in structural steganalysis. © 2013 Springer-Verlag.