Robust, secure, efficient, and imperceptible, for a seamless viewing experience.
The following characteristics are desirable for forensic watermarks:
- Imperceptibility: A forensic watermark should not be audible or visible. To a human, a forensically watermarked media object should be indistinguishable from the unwatermarked original.
- Robustness: Even if an attacker knows that a media object is watermarked, it should be infeasible to remove the watermark without unacceptably damaging the host media in the process.
- Capacity: A good forensic watermark is capable of storing a large payload, as measured in bits of information.
- Security: It should be infeasible for an attacker to modify the payload of the watermark, or create a falsely watermarked media object.
- Efficiency: It should take as little computational time as possible to embed and extract the watermark into and from a media object.
Note that it is always possible to remove a forensic watermark if the media is damaged sufficiently – one could reliably remove a video’s watermark by making all pixels in all frames black. However, this would render the video unusable. A practical measure of robustness is the extent to which media must be damaged to no longer make the watermark readable.
Forensic watermarking is quickly becoming ubiquitous in the industry, but it is not new. Analog watermarks date back to the 13th century, when they were first applied to paper documents. Subaudible tones used for synchronization in film strip projectors in the 1970s are an early example of audio watermarks used in other types of media. However, digital watermarking was first introduced in 1993 and was used to embed information into images. Philips launched their session-based forensic video watermark in 2007, which made it possible to embed viewer information directly in a pay-TV subscriber’s set-top box. Since then, the use of session-based forensic watermarks have become a common way to track the source of infringed content.
Because forensic watermarks do not have the requirement of being readable by humans, they have various valuable features:
- They do not need to deteriorate the viewing experience.
- They can be hard to detect for someone who wants to destroy it.
- It is hard to know when they have been destroyed.
- They can be spread over the screen and frames.
Custos provides a session-based forensic video watermark that is specifically designed to be readable by a publicly available extractor tool. The watermark is built to be highly imperceptible (even in high dynamic range content), robust against the most destructive attacks like heavy video compression and “cam ripping”, and very fast to embed. It also has an exceptionally high payload capacity of 256 bits.