The Watermarking Requirements

A watermarking application is entitled to its own specific requirements. Though there is no set of requirements to be met by all watermarking techniques, some general directions can be given for most of the applications mentioned in the first chapter. 

In most applications the watermarking algorithm must embed the watermark such that this does not affect the quality of the underlying host data. Awatermark-embedding procedure is truly imperceptible if humans cannot distinguish the original data from the data with the inserted watermark. Even the smallest modification in the host data may become apparent, however, when the original data is compared directly with the watermarked data. Since users of watermarked data normally do not have access to the original data, they cannot perform this comparison. Therefore, it may be sufficient that the modifications in the watermarked data go unnoticed as long as the data are not compared with the original data.