Abstract
When looked at as a communication task, the
watermarking process can be split into three
main steps: watermark generation and embedding
(information transmission), possible attacks
(transmission through the channel), and watermark
retrieval (information decoding at the
receiver side). In this article we review the main
issues in watermark generation and embedding.
By focusing on the case of image watermarking,
we first discuss the choice of the image features
the watermark is superimposed to. Then wc consider
watermark generation and the rule used to
insert the watermark within the host features. By
adopting again a communication perspective,
some useful hints are given on the way the watermark
should be shaped and inserted within the
host document for increased robustness against
attacks. Given that invisibility is one of the main
requirements a watermark must satisfy, the way
psycho-visual notions can be used to effectively
hide the watermark within an image is carefully
rcviewed in the second part of the article. Rather
than insisting on the mathematical aspects of
each of the above issues, the main rationale
behind the most commonly adopted approaches
is given, as well as some illustrative examples.
