Machine Learning in Image Steganalysis

Chapter 5

Bit-plane Analysis

The study of individual bit planes is one of the most classic approaches to steganalysis. By bit plane i we mean the binary image which is obtained by taking only bit i from the binary representation of each pixel. Thus, the eighth bit plane of an 8-bit image is the pixmap reduced modulo two, also known as the LSB plane.

We saw the first example of bit-plane analysis, in the context of visual steganalysis, in Figure 2.4. In this chapter we shall see that bit-plane analysis can also form the basis for features to be used in machine learning. However, to understand the artifacts the features are designed to capture, it is helpful to start with more visual steganalysis.

5.1 Visual Steganalysis

The visual attack from Figure 2.4 is very well known in the literature. It may therefore be surprising that there has been little discussion of when it is appropriate and when it is not. A novice trying to repeat the experiments of classic authors will often struggle. Far from all images will show the nice structure which is so evident in Figure 2.4.

Code Example 5.1 : Given an 8-bit image X in the form of a numpy array, return an 8-bit image representing the bth bit plane

def bitplane(X,b):
    b = 8 − bp
    return 255*((X>>b)%2)

Figure 5.1 shows another example. The image is taken with the same camera, and converted and embedded in the exact same way as the image in Figure 2.4. Some structure is seen in the LSB plane of the palette image, but not as much as in the ...