Hiding and Seeking Class Discrimination Lyu and Farid use class discrimination to detect hidden content. [Farid, 2001] [Lyu et al., 2002] Distinguish between two cases: stego image and non-stego image. Feature vector from wavelet-like decomposition results in higher-order statistical model of images. Collect feature vectors from training set to determine discrimination function. 1,800 images in training set. Cannot determine length of hidden message. Non-linear Support Vector Machine (SVM) finds discrimination function.