  This paper proposes a new steganographic scheme relying on the principle of
cover-source switching, the key idea being that the embedding should switch
from one cover-source to another. The proposed implementation, called Natural
Steganography, considers the sensor noise naturally present in the raw images
and uses the principle that, by the addition of a specific noise the
steganographic embedding tries to mimic a change of ISO sensitivity. The
embedding methodology consists in 1) perturbing the image in the raw domain, 2)
modeling the perturbation in the processed domain, 3) embedding the payload in
the processed domain. We show that this methodology is easily tractable
whenever the processes are known and enables to embed large and undetectable
payloads. We also show that already used heuristics such as synchronization of
embedding changes or detectability after rescaling can be respectively
explained by operations such as color demosaicing and down-scaling kernels.
