The thesis takes into account steganography and steganalysis in the pixel domain. The contribution of this thesis is threefold.*From a steganalysis point of view we introduce a new steganalysis method called Amplitude of Local Extrema (ALE) which outperforms previously proposed pixel domain methods. As a second contribution we introduce a comparative methodology for the comparison of different steganalyzers and we apply it to compare ALE with the state-of-art steganalyzers. The third contribution of the thesis regards steganography, since we introduce a new embedding domain and a corresponding method, called MPSteg-color, which outperforms, in terms of undetectability, classical embedding methods as ±1 embedding.