Digital Watermarking
Digital watermarking is distinctly different from data hashing. It is the process of altering the original data file, allowing for the subsequent recovery of embedded auxiliary data referred to as a watermark.
A subscriber, with knowledge of the watermark and how it is recovered, can determine (to a certain extent) whether significant changes have occurred within the data file. Depending on the specific method used, recovery of the embedded auxiliary data can be robust to post-processing (such as lossy compression).
If the data file to be retrieved is an image, the provider can embed a watermark for protection purposes. The process allows tolerance to some change, while still maintaining an association with the original image file. Researchers have also developed techniques that embed components of the image within the image. This can help identify portions of the image that may contain unauthorized changes and even help in recovering some of the lost data.
A disadvantage of digital watermarking is that a subscriber cannot significantly alter some files without sacrificing the quality or utility of the data. This can be true of various files including image data, audio data, and computer code.
Read more about this topic: Watermark (data File)