Media that is distributed digitally can be copied and redistributed illegally. Embedding an individual watermark in the media object for each customer will make it possible to trace pirate copies to the redistribution source. However, digital distribution methods such as broadcast and multicast are scalable and will give all customers identical copies of the media content. Distribution of individually watermarked media is more difficult to achieve. In this chapter, methods for how media with individual watermarks can be distributed scalable are presented and discussed. These methods are categorized in four groups. One group that is based on watermark embedding in the network, another group for embedding in the client, and two groups that use fragments of the media content that are unique for each customer or shared among a subgroup of customers.
In this section the background to watermarking is given. Compression and distribution algorithms are also discussed.
Key Terms in this Chapter
Sparse Watermark: Watermarks that are embedded so that a large part of the media object is needed to extract the watermark.
Dense Watermark: Watermarks that are embedded in such way that only a small part of a large media object is needed to extract the watermark.
Multicast: The distributor transmits one packet that reaches all customers belonging to a multicast group.
Compression: Decreasing the amount of data needed to describe a media object. If distortion is added to the media during compression the method is lossy.
Watermarking: The embedding of a mark within a media object. The mark can later on be retrieved from the media.
Scalable Distribution: A distribution method that does not need to transmit the same content many times to reach all recipients, like multicast and broadcast.
Broadcast: The distributor transmits one packet that reaches all customers.
Individual Watermarking: The embedding of a unique mark for each copy of a media object, also known as Fingerprinting.
Unicast: The distributor transmits one packet to each customer.