Investigators Guide to Steganography

Proof of Ownership

One major application of digital watermarking is to convey ownership. By saying that, we are also saying that there is someone who may try to take the material and misuse it by removing the ownership information. Proof of ownership information may take two forms. First, the watermark may identify the owner of the material, or second, it may identify the recipient to whom the material was given. Adding to that, these watermarks may be visible or invisible. All four possibilities make sense in the proof-of-ownership concept and all have been used in real systems.

Consider the first form of proof of ownership, watermarking the owner, and some of its benefits. A visible watermark can act as advertising by creating an unbreakable link between the image and the creator. This unbreakable link can also restrict the use of the image because no matter where it is used, everyone knows who created it, discouraging misuse. An invisible watermark could be used in a much more subtle way; it could be used as a "tag" that allows you to search the Web for your image to see if it is being misused.

Captioning is another way to watermark the owner, although this method does not necessarily act as a deterrent. Captioning embeds the watermark in the material together with associated information, for example, name, author, date, point of contact, etc. This information is usually useful to everyone. This type of watermarking is particularly good for auditing and verification. For example, a song with an inaudible watermark could be monitored to determine how many times the song is played on the radio and that it matches up with the contract the radio station signed. It could also be used to ensure that a radio or television advertisement is run the appropriate number of times.

With the explosion of DVDs in the marketplace, the movie industry has taken a strong interest in watermarking its product to prevent unauthorized copying. Tags in the watermark combined with a hardware-enabled player could allow a DVD to carry instructions to "copy never" or "copy once," allowing a user to make a backup but not unlimited copies of the DVD.

Another way is to watermark the recipient to whom the material was given or sold. This type of watermarking has raised a lot of invasion-of-privacy issues, but in reality the invasion of privacy would only come about if the recipient does not follow the agreement of the received material, meaning it should not be widely redistributed.

Secure Distribution

Using a watermark for secure distribution can provide a good deal of flexibility to the owner and distributors of the product. For example, using a watermark for secure distribution could ensure that digital contents arrive at the consumer without changes en route; it could ensure that the distributor gets paid, that the consumer's payment mechanism and privacy is protected, and that the distributor retains control of further distribution and use of the content.