Hiding and Seeking
               Attacking the OutGuess

Fridrich et al. find steganalytic method to detect OutGuess independent of the DCT histogram.

[Fridrich et al, 2002]       

Discontinuities along the pixel block boundaries increase with the length of the hidden message.
Blockiness measure:


Determine blockiness of cover image by cropping and recompressing stego image!

Calculate length of hidden message by embedding more hidden data into stego image and recovered cover image.
Advantage compared to class discrimination.