Steganalysis with JPEG and GIF images

Steganalysis methods for detecting secret message embedded in JPEG and GIF images are presented in this paper. Usually, the DCT coefficients are modified when secret data is embedded to JPEG images, and the pixel indexes are changed in GIF data hiding. No matter it is the DCT coefficients or image pixel changed in data hiding, the introduced noise deteriorates the smoothness of images. For JPEG images, the change of smoothness at the block boundary is used to distinguish the clean and stego images. For GIF images, the change of smoothness between neighbor pixels is used in steganalysis. For stego GIF images created by reordering colors in the palette, we discriminate the stego and clean images by checking the palette to see if there is a pattern existing or not.