“…We note that the bootstrap samples are formed "by pairs," i.e., we make sure that the pairs of cover features and the corresponding stego features are preserved. This modification, which is specific for steganalysis, is rather important as it has been shown that breaking the coverstego pairs into two sets, one of which is used for training and the other, testing, one for error estimation, may lead to a biased error estimate and, consequently, to a suboptimal performance [46], [27].…”