Digital watermark

From Just Solve the File Format Problem
Jump to: navigation, search
File Format
Name Digital watermark

A digital watermark is a kind of digital signature, usually in the form of a subtle modification to the main content of an image, audio, or video file. To put it another way, a digital watermark stores metadata inside the main content of a file, instead of separately. There are a number of different reasons for using a watermark, but the main point is to make it difficult to remove the metadata.

A digital watermark could be anything from a clearly visible overlayed semi-transparent copyright notice, to a steganographic technique that makes the signature virtually undetectable, or anything in between. It could be a simple notice of what software created the file, or it could contain detailed tracking information intended to help figure out who created the file.

There are 2 main features that separate a watermark from general steganography

  • Size of data: Steganography is concerned with hiding data, typically whole files. Watermarks are only concerned with having just enough data to ID the file/sender/etc. The small amount of data opens up more areas and ways to hide data that wouldn't be practical with larger files.
  • Robustness: Steganography is typically very fragile to any editing of the file, while a watermark should ideally be very difficult to get rid of. For instance, a watermark hidden in an image file should be robust enough that format conversions, resizing, cropping, etc don't impact the ability to read that data.

Similar to bar codes, some kinds of watermarks store digital data in physical/analog documents. See Watermark (physical).



Format Info

Office Open XML

See also


Personal tools