1. A method for steganalysis of an image comprising: directly decomposing a two-dimensional (2-D) spatial representation of the image into multiple size non-overlapping, N×N block decompositions of the two-dimensional (2-D) spatial representation of the image; applying N×N block discrete cosine transforms (BDCT) to each of the non-overlapping, N×N block decompositions, to obtain a BDCT 2-D coefficient array corresponding to each N×N block; extracting moments using characteristic functions derived based on the spatial representation of the image and each of the BDCT coefficient 2-D arrays, to obtain extracted moments; generating features based at least on the extracted moments, to obtain generated features; and classifying the image based at least on the generated features; wherein the applying and extracting are performed for at least two different values of N.