Digital Watermarking—A Specialized Form of Digital Steganography

In classifying digital watermarking programs as digital steganography applications, it is important to distinguish between watermarking programs that embed a visible watermark and those that embed an invisible watermark. Because the objective of steganography is to conceal the existence of information, a watermarking program that embeds a visible watermark in the carrier file could hardly be considered a steganography application. However, a watermarking program that leaves an invisible watermark in the carrier file should be properly classified as an application of digital steganography because the embedded watermark is imperceptible to the human senses.

Another characteristic of digital watermarking programs is robustness.

A watermark is considered to be fragile if the mark is not detectable after even the slightest transformation of the carrier file. For example, resizing an image file could destroy a fragile watermark. On the other hand, a watermark is considered to be robust if the mark is detectable after certain transformations are performed on the carrier file. Thus, digital watermarking programs that embed robust imperceptible watermarks must be properly classified as digital steganography applications. Another aspect of digital watermarking programs is the size of the payload that can be embedded in the carrier file. The payload size of a digital watermarking program will be much more restricted than the payload size of other digital steganography applications.Many steganography applications can accommodate multi-megabyte payloads. However, a digital watermarking program may only embed a few bytes or a few hundred bytes. The quantity of information that can be embedded in a carrier file is not a good criterion for determining whether or not an application should be considered a steganography application. It is not difficult to imagine scenarios where a single word or number could have a much larger meaning. Therefore, even though digital watermarking programs have restricted payload capability, the programs that employ techniques to embed robust and imperceptible watermarks must be classified as digital steganography applications It is important to note that some steganography investigation datasets do not include any digital watermarking programs because the dataset creators do not consider any digital watermarking programs to be steganography applications even if the program embeds a robust imperceptible watermark. Therefore, digital forensics examiners must be careful when determining which steganography data set to use because selecting the wrong one could result in failure to detect certain digital watermarking programs that may have been used to hide information of evidentiary value in a criminal investigation.

At Backbone Security, we include digital watermarking programs that embed a robust and imperceptible watermark in our Steganography Application Fingerprint Database (SAFDB). Because the watermark embedded by these programs is not detectable by the Human Visual System, it meets our criterion for classification as a digital steganography application.

SAFDB is maintained in our Steganography Analysis and Research Center (SARC) and is the world’s largest hash set exclusive to digital steganography applications.

Jim Wingate is Director of the Steganography Analysis and Research Center and Vice President of Backbone Security and welcomes your views on the proper classification of digital steganography applications.

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