Practical capacity of digital watermarks

A practical approach for evaluating the capacity of watermarks is presented.
In real applications of watermarks, reliability is one of the most important
metrics. The problem focused on in this paper is maximizing the number
of embedded bits when there are some constraints on detection reliability. Error
rates are formulated under some assumptions about the watermarking scheme,
and the capacity can be determined by setting the bounds on each error rate. Experiments
are performed to verify the theoretical predictions using a prototype
watermarking system which conforms to the assumptions, and the resulting capacity
agrees with the theory. Further, the theoretical effects of employing error-correcting
codes are considered. It is shown that this approach yields the practical
capacity of watermarks, as compared with channel capacity in communication theory.