Machine Learning in Image Steganalysis

Chapter 4

Histogram Analysis

Analysis of the histogram has been used in steganalysis since the beginning, from the simple pairs-of-values or χ² test to analysis of the histogram characteristic function (HCF) and second-order histograms. In this chapter, we will discuss a range of general concepts and techniques using the histogram in the spatial domain. Subsequent chapters will make use of these techniques in other domains.

4.1 Early Histogram Analysis

The histogram was much used in statistical steganalysis in the early days, both in the spatial and the JPEG domains. These techniques were targeted and aimed to exploit specific artifacts caused by specific embedding algorithms. The most well-known example is the pairs-of-values or χ² test, which we discussed in Section 2.3.4.

None of the statistical attacks are difficult to counter. For each and every one, new embedding algorithms have emerged, specifically avoiding the artifact detected. Most instructively, Outguess 0.2 introduced so-called statistics-aware embedding. Sacrificing some embedding capacity, a certain fraction of the coefficients was reserved for dummy modifications designed only to even out the statistics and prevent the (then) known statistical attacks.

A key advantage of machine learning over statistical attacks is that it does not automatically reveal a statistical model to the designer. The basis of any statistical attack is some theoretical model capturing some difference between steganograms and natural images. ...