- Digital multimedia (e.g. digital audio and video) has this advantage that they can be easily copied without losing quality. But this advantage is also a problem for information providers: people can copy their works without obeying the copyright rules.
- Copyright protection is a complicated issue in the digital world. One aspect of the issue is how to prove the ownership of a particular work. For e.g., an image.
- The common approach to prove ownership is to use a process called watermarking, which embeds an invisible label, mark, or signature (called a watermark) into an image or video.
- When conflict arises, the embedded signature is extracted to prove the rightful ownership.
- To be useful, the watermark should be recoverable despite intentional or unintentional modification of the image. That is, the watermark should be robust against image processing operations such as filtering, scaling, cropping, and compression.
- It must also be invulnerable to deliberate attempts at forgery and removal.
- Distribution tracking is made possible by letting seller insert a distinct watermark, which is called a fingerprint, identifying the buyer, or any other address of the work, within any copy of data that is distributed.
- If an unauthorized copy of the protected works is found, then its origin can be recovered by retrieving the unique watermark contained in it.
- Figure below shows a specified scheme exemplifying a fingerprint protocol (the numbers indicate the sequence of operations).
- Before the multimedia document is legally acquired, the buyer has to provide his own identifier to the seller.
The seller embeds this identifier into the document and gives it to the buyer.
If the buyer illegally distributed the acquired content to another party, a control authority can detect his identifier into the document and take actions against him.
- The main requirement set by the fingerprinting application is security, since any attempt to remove the watermark or making it unreadable must be prevented.
- When copy deterrence is not sufficient to effectively protect legitimate rights holders, a true copy protection mechanism must be envisaged.
Digital watermarking may be used for a wide range of applications, such as:
- Copyright protection
- Source tracking (different recipients get differently watermarked content)
- Broadcast monitoring (television news often contains watermarked video from international agencies)
- Video authentication
- Software crippling on screen casting programs, to encourage users to purchase the full version to remove it.