1 Digital Water Marks

2 History The Italians where the 1 st to use watermarks in the manufacture of paper in the 1270's. A watermark was used in banknote production by the Bank of England in It is a good security feature because the watermark cannot be photocopied or scanned effectively.

3 Why Watermark? Motivation (1/2) The rapid revolution in digital multimedia and the ease of generating identical and unauthorized digital data. For example: USA Today, Jan. 2000: Estimated lost revenue from digital audio piracy $8,5 billions Digital objects can be copied and distributed, transmitted, manipulated anonymously with no way to identify the criminals. Copyright protection of multimedia data Copyright owners want to be compensated every time their work is used.

4 Why Watermark? Motivation (2/2) The need to limit the number of copies created whereas the watermarks are modified by the hardware and at some point would not create any more copies (i.e. DVD) - the reading device must be able to modify the watermark Content protection – content stamped with a visible watermark that is very difficult to remove so that it can be publicly and freely distributed

Definition Digital watermarking is the act of hiding a message related to a digital signal (i.e. Text, an image, song, video) within the signal itself to show authenticity or proof of ownership

Watermarking applications Broadcast monitoring. Owner identification, instead of including copyright notices with every image or song, we could use watermarking to embed the copyright in the image or the song itself.

Watermarking applications Transaction tracking. In this case the watermark embedded in a digital work can be used to record one or more transactions taking place in the history of a copy of this work. For example, watermarking could be used to record the recipient of every legal copy of a movie by embedding a different watermark in each copy. If the movie is then leaked to the Internet, the movie producers could identify which recipient of the movie was the source of the leak.

Watermarking applications Copy control, watermarking can be used to prevent the illegal copying of songs, images or movies, by embedding a watermark in them that would instruct a watermarking-compatible DVD or CD writer to not write the song or movie because it is an illegal copy.

9 Some Digital Watermarking Types (1/2) Visible vs. Invisible: Visible such as a company logo stamped on an image or Video. Invisible intended to be imperceptible to the human eye or inaudible. the watermark can only be determined through watermark extraction or detection by computers. Fragile vs. Robust : Fragile watermarks break down easily. Robust survive manipulations of content.

10 Some Digital Watermarking Types (2/2) ● Public vs. private – Private watermarking techniques require that the original be used as a basis of encryption whereas public does not

11 Some Desired Properties of (DW) ( 1/3) 1. Robustness 2. Tamper Resistance 3. Economically Implementable 4. Unambiguous 5. Capacity 6. Quality

12 Desired Properties ( 2/3) (1) Robustness: A watermark must be difficult or impossible to remove, at least without visibly degrading the original image. A watermark must survive image modifications. Geometric distortions: rotation, scaling, translation, etc. (2) Tamper Resistance: The watermark must resist any type of attacks, what ever the intentions are: remove or modify

13 Desired Properties ( 3/3) (3) Economically implementable: Time and effort, cost. ( 4) Unambiguous: The watermark, when retrieved, should unambiguously identify the owner. (5) Capacity: The amount of information that can be embedded (6) Quality: (High Quality) - Quality not degraded

14 Properties Tradeoff Robustness Capacity Quality Embedding and Extraction Complexity

15 Important Definitions Cover : Audio-video, text in which data will be hidden Watermark: What is actually added to the cover Information: message to be added Watermarking key: Secret parameter needed for embedding & detecting the watermark & extracting the information Watermarking Function: Embedding & Extraction algorithms.

16 Watermarking Embedding & Extraction Cover Image Cover + WM F Embedding F : Watermarked Image = Function (Cover, Watermark, Key) F Extraction F : Watermark = Function (Watermarked Image, Key( Cover + WM

17 Attackers Main Goal Attackers seek to destroy watermark for the purposes of use without having to pay royalties to the originator of the content.

18 Why do we need to study attacks? Identify weakness Propose improvement – Security Attackers are knowledgeable, creative, have lots of time, and are numerous

19 Attacks on Watermarking Two Sets of Attacks Unintentional All image manipulations commonly used to prepare images for print publication. For example: Resizing, rotation, sharpening, contrast modification, compression, ect. Intentional (Malicious) All the well-known intentional attacks include: Disabling, altering, embedding new watermark, ect.

20 Intentional Watermark Attacks (1/2) Active Attacks – hacker tries to remove the watermark or make it undetectable. Applying Geometric transformation: rotation, scaling, translation, change aspect ratio. Passive Attacks – hacker tries to determine whether there is a watermark and identify it. However, no damage or removal is done. Collusion Attacks – hacker uses several copies of one piece of media, each with a different watermark, to construct a copy with no watermark.