Steganography by Synthesis: Can Commonplace Image Manipulations Like Face Morphing Create Plausible Steganographic Channels?

From the three basic paradigms to implement steganography, the concept to realise the information hiding by modifying preexisting cover objects (i.e. steganography by modification) is by far dominating the scientific work in this field, while the other two paradigms (steganography by cover selection or -synthesis) are marginalised although they inherently create stego objects that are closer to the statistical properties of unmodified covers and therefore would create better (i.e. harder to detect) stego channels. Here, we revisit the paradigm of steganography by synthesis to discuss its benefits and limitations on the example of face morphing in images as an interesting synthesis method. The reason to reject steganography by modification as no longer suitable lies in the current trend of steganography being used in modern day malicious software (malware) families like StuxNet, Duqu or Duqu 2. As a consequence, we discuss here the resulting shift in detection assumptions from cover-only- to cover-stegoattacks (or even further) automatically rendering even the most sophisticated steganography by modification methods useless. In this paper we use the example of face morphing to demonstrate the necessary conditions1 'undetectability' as well as 'plausibility and indeterminism' for characterizing suitable synthesis methods. The widespread usage of face morphing together with the content dependent, complex nature of the image manipulations required and the fact that it has been established that morphs are very hard to detect, respectively keep apart from other (assumedly innocent) image manipulations assures that it can successfully fulfil these necessary conditions. As a result it could be used as a core for driving steganography by synthesis schemes inherently resistant against cover-stego-attacks.