FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
SUBJECT FORENSIC SCIENCE
Paper No. and Title PAPER No.7: Criminalistics and Forensic Physics Module No. and Title MODULE No.34: Digital Watermarking
Module Tag FSC_P7_M34
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
TABLE OF CONTENTS
1. Learning Outcomes 2. Introduction
3. Digital Watermarking
4. Incorporation of Watermarks in Digital Image 5. Significance of Watermarks in Digital Photography 6. Working of Digital Watermarks
7. Categories of Digital Watermarking 8. Image Authentication
9. Content Protection and Digital Watermarking 10. Forensics and Piracy Deterrence
11. Broadcast Monitoring 12. Summary
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
1. Learning Outcomes
After studying this module, you shall be able to know about-
The significance of digital watermarking
The incorporation of watermarking to a digital image
The various categories of digital watermarks
2. Introduction
The term “Digital Watermarking” follows the term watermarking which is believed to have been incepted long back. Watermarks are distinguishing marks or designs or patterns impressed on paper during manufacturing process, by making thinner (line or wire watermarks) or thicker (shadow watermarks) on the layer of pulp when it is still wet. Watermarks are visible when paper is held up to the light or in some cases, over a black surface. (E.g. currency note, bond paper, stamps etc.). The objective of watermarks in paper is, essentially identifying the paper as a signature of the manufacturer or as a security measure to avoid forgery of important documents. The foundation of the water part of watermark can be traced to a time when it was something which was only present in paper. During those times, a watermark was formed by changing the paper thickness and hence, forming a shadow or lightness in the watermarked paper. This was done while the paper was still wet or watery and therefore the mark created by this process is called a watermark. Undeniably, watermarks can be of help in studying the age old documents because they can suggest their origin or date.
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
Cigarette Paper
Official Papers
Currency Notes
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
Initial application of watermarking was also information hiding for Passing Secret messages. Information hiding started with Steganography is the art and science of concealing messages into something innocuous in such a way that it is extremely difficult for someone to suspect, let alone find, except intended recipient knows of the existence of the hidden message.
3. Digital Watermarking
Digital watermarking is the process by which identifying data is woven into media content such as images, movies, music or other multimedia data with a specific algorithm imparting the objects with an exceptional, digital identity which can therefore be used in various applications. Though a digital watermark is indiscernible to the human senses and nevertheless simply documented by special software detectors, it remains constant even after being recorded, manipulated and edited, being compressed or decompressed, encrypted, decrypted and broadcasted, without the content quality being affected. A digital watermark added to a photo, is more or less visible information in the form of a text or some other photo/image that has been added to the original photo. The added information can be more or less transparent to make it either easy or hard to notice the watermark.
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
So a digital watermark is a lot like the metadata that is invisible and attached to an image.
Unlike metadata, it is much more difficult to remove and it stays with an image even through all types of manipulation like copying, cropping, editing, compression and decompression, encryption and decryption without affecting the quality of the image.
4. Incorporation of Watermarks in Digital Image
In a photograph the addition of a transparent watermark is done by changing the image at the level of pixel wherein a pixel represents one dot of an image. The pixels that will make up the resulting watermark is changed more or less in the direction of the watermarking image, if for example the watermark is 50% transparent, 50% of the RGB (Red, Green & Blue) values are deducted from the original image, and 50% of the RGB values from the watermark are added to the image.
5. Significance of Watermarks in Digital Photography
A watermark is added on a digital photograph with the intention that it should not be copied or used without the consent of the author or the originator. Also if a highly visible watermark is added along with an almost hidden one, it will be much more easy for the thief to overlook the invisible and thereby adding more protection of the images.
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
A lot of research has been carried out so that an invisible watermark can be added to the image which is difficult to remove again; many of these programs do not work on JPEG images since these are transformed in the compression of the image. Many companies are working on the option of adding a hidden watermark to the image.
Digital watermarking algorithm is of three parts:
a. Watermark embedding algorithm b. Watermark extraction algorithm c. Watermark detection algorithm
Digital watermarking is a technology that opens new door for users, whether watermark can be reliably detected after performing some media operations.
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
i. Perceptual transparency
This property describes that whether watermark is visible or invisible to human sensor organ. Perceptible watermarks are defined as those watermarks which are visible to the human sensory organ. The imperceptible watermarks are defined as those watermarks which cannot be visualized and in these, the contents remain unchanged even after the application of the technique of digital watermarking. Perceptible watermarks i.e. visible one are extension of the concept of logos. They are applicable to images only. These watermarks are embedded into image. They are applicable in maps, graphics and software user interface. Imperceptible watermarks are useful for content or author authentication and for detecting unauthorized copier.
ii. Security
Security property describes that how easy to remove a watermark. This is generally referred to as “attack” on watermarking. Attack refers to detection or modification of watermark.
iii. Complexity
This is an important property which is to be considered in Real time applications like video. Complexity property is concerned with amount of effort needed to extract or retrieve the watermark from content.
iv. Capacity
Capacity property of digital watermarks refers to amount of information that can be embedded within the content. If more data is used in watermark, it will become less robust.
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
v. Robust watermarks and fragile watermarks
Robust or fragile is the degree wherein a watermark is able to withstand any sort of change which is caused because of lossy or transmission compression. The imperceptible watermarks are less robust as compared to the perceptible one. Robust watermarks are defined as those watermarks which when embedded in an object are difficult to remove whereas fragile watermarks can be defined as those which can easily be destroyed, if any tampering is done with them. Also, once there is manipulation of data, the fragile watermarks will get destroyed by it.
vi. Private watermarks and public watermarks
Private watermarks need at least unique data to improve watermark information. Public watermarks require no real data and implanted watermarks to pull through watermark information. Private watermarks are also known as secure watermarks. To read or retrieve private watermark, it is essential to have secret key. Public watermark can be read or retrieved by anyone using specialized algorithm.
6. Working of Digital Watermarks
Digital watermarks offer the way of escaping steganographic messages for many different purposes.
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
• Data (D), Watermark (W), Stego Key (K), Watermarked Data (Dw) Embed (D, W, K) = Dw
Extract (Dw) = W‟ and compare with W
(E.g. find the linear correlation and compare it to a threshold)
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
How do we make this system secure?
A. Stego Key or K is secret (Use cryptography to make information hidden more secure)
Example – Embedding (DW = D + W)
• Matrix representation (12 blocks – 3 x 4 matrix)
(Algorithm Used: Random number generator RNG), Seed for RNG = K, D = Matrix representation, W = Author’s name
Example – Extraction
• The Watermark can be identified by generating the random numbers using the seed K
Data Domain Categorization
• Spatial Watermarking
Through application of data to implant and remove Watermark E.g. voltage values for audio data
• Transform Based Watermarking
Conversion of data to another format to embed and extract.
E.g. Transformation to polar co-ordinate systems of 3D models, creates it forceful against scaling
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
Extraction Categorization
• Informed (Private) : Extract using {D, K, W}
• Semi - Blind (Semi-Private) : Extract using {K, W}
• Blind (Public) : Extract using {K}
- Blind (requires less information storage)
- Informed techniques are more robust to tampering Robustness Categorization
• Fragile (for tamper proofing e.g. losing watermark implies tampering)
• Semi-Fragile (tough in contradiction of operator level processes, e.g. image compression)
• Robust (counter to challenger grounded attack, e.g. noise possession to images) Categorization of Watermark
Eg1. Robust Private Spatial Watermarks Eg2. Blind Fragile DCT based Watermarks Eg3. Blind Semi-fragile Spatial Watermark
7. Categories of Digital Watermarking Spatial Domain Method
The spatial domain is the normal image space, in which a change in position in I directly projects to a change in location in space. Distances in I (in pixels) relate to actual distances (e.g. in meters) in space. This notion is most often used while taking into account the frequency at which the value of image changes, i.e. when does the repeating intensity variations occur depending upon the pixels.
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
Transform Domain Method
High quality watermarked image is produced by this method in which the original image is first transformed by use of DCT or Discrete Cosine Function, DWT or Discrete Wavelet Transform and Fourier into its frequency domain. Thus, in this method the marks are added to the values of its transformed coefficients and not to the image intensity. The watermarked image is formed by inversing the marked transformed coefficient. The use of frequency based transforms allows the direct understanding of the content of the image. Hence, HVS or features of the Human Visual System (HVS) can then be consider when it is phase to select the concentration and location of the watermarks to be made functional to a given image.
Least Significant Bit
The easiest method in digital watermarking is in spatial domain applying the two dimensional display of pixels in the container image to hold hidden data using the Least Significant Bits (LSB) method.
The stages to insert watermark image are given below.
Steps of Least Significant Bit
Transform RGB image to gray scale image.
Create twin exactness for image.
Shift most significant bits to low significant bits of watermark image.
Create less noteworthy bits of host image to zero
Enhance cleaned version of watermarked image to altered host image.
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
Limitations of Spatial Domain Watermarking
In any watermarking application, this method lacks robustness and is relatively simple. In addition to the noise factor, it can also survive simple operations like cropping but the watermark is defeated by the lossy compression. To have negligible impact on the cover object the LSB bits can then be set to „1‟ and moreover, the watermark can be altered by an intermediate party once the algorithm is discovered.
Discrete Cosine Transform Watermarking
The DCT permits an image to be fragmented into dissimilar frequency bands, making it very easier to insert watermarking information into the middle frequency bands of an image. The middle frequency bands are selected so that they have diminished, they escape the most graphic imperative portions of the image devoid of over-exposing themselves to removal through firmness and clatter attacks.
Steps of DCT watermarking
The elementary notion in the DWT for a one dimensional signal is that a signal is divided into two portions, generally high frequencies and low frequencies. This procedure is a continuous chance of number of intervals, which is generally known by the applying at instance.
Steps of DWT watermarking
i. The main measure of the watermarking process is, basically the encoder. The first stage is to molder the image into 4 frequency bands by applying first purpose of Haar wavelets at this state.
ii. In succeeding phase, molder image into 7 frequency bands by applying subsequent resolutions of Haar wavelets. At next level, molder image in to 10 frequency bands by applying third resolutions of Haar wavelets and so on.
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
iii. The afterward process is to give a pseudo arbitrary sequence N, Gaussian distribution of mean zero and variance one, to the coefficients of the medium and high frequency bands.
iv. The normal distribution is used because it has been proven to be quite robust to collusive attacks.
Digital Watermarking Applications
Copyright Protection: To prove the ownership of digital media.
Hidden watermarks represent the copyright information.
Tamper proofing: To find out if data was tampered. Eg. Change meaning of images.
Hidden watermarks track changes in meaning.
8. Image Authentication
At first, a semi-fragile watermarking in embedded into the image for authentication and reliability inspection resolutions by applying a QIM scheme assimilated in a JPEG2000 coder next, the image is JPEG compressed at default quality level (in order to simulate a common unintentional attack) and then maliciously manipulated using the Gimp.
9. Content Protection and Digital Watermarking
It offers an additional sheet of safety to the content protection chain to deter unauthorized use of content by inserting watermarks that recognize the acceptable application of the content into the music or motion picture soundtrack prior to theatrical, packaged media (Blu-ray Discs, DVDs) and online digital distribution.
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
10. Forensics and Piracy Deterrence
Forensic watermark tool applied to improve a content possessor's capability to perceive and reply to mismanagement of its possessions. Forensic watermarking is applied not only to collect evidence for legitimate measures, but also to impose prescribed usage contracts between a content owner and the individuals or corporations with which it shares its content. It offers progressive, irrefutable evidence of misuse for leaked content assets. Watermarking can also counterpart Digital Rights Management (DRM), by harmonizing content proprietor patents with customer reasonable use allowances.
Working procedure
A forensic application embeds the identity of a recipient into an asset copy (Forensic Report) at the time it is produced or transmitted. Sophisticated forensic advantage insert situational metadata like as broadcast time, received format, and recipient IP address.
Some watermark applications embed a distinct forensic watermark at each stage of content distribution, enabling pinpoint accuracy. When a leak is discovered or suspected, the forensic watermark retrieved from the leaked copy identifies the intended recipient and provides evidence in the form of situational metadata that the copy was delivered to its intended destination. The evidence can be used to trigger contractual provisions or as legal evidence in a criminal action.
Use of digital watermarking for forensics & piracy deterrence helps companies
Create a powerful deterrence from leaking content either maliciously or unintentionally.
Quickly and accurately identify the source of leaked content.
Provide irrefutable evidence of content misuse in support of legal action.
Gain visibility over where and how their content is being accessed without the need of a complete DRM system to restrict access.
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
Content Filtering (includes Blocking and Triggering of Actions)
The experience of watching television has radically changed over the last few years.
Today people want to watch content in their own time and place. Digital watermarks offer new opportunity for content possessors, promoters and very commonly marketers who are in search for innovative methods to engross customers with richer media experiences from the STB and Television set.
Copyright Communication and Digital Watermarking
Watermarks stay with content as it is forwarded and travels across the internet and can be detected at any point to determine the content's unique identity. Watermarks also persist in various diverse file managements and conversions, contrasting usual metadata which is frequently missing, making the content "orphaned."
Effective copyright communication helps content owners
Ensure their ownership and contact information stays permanently attached to their content wherever it may travel and be accessed on the web or packaged media.
Monetize their content, with opportunities to add automated licensing to increase revenues.
Better managing of content through a range of automated remedies when unauthorized use is discovered, including device enforcement messages of copyright policies, take down notices or providing permission with proper attribution.
Protect their content from being an "orphaned work" whose origin is unknown.
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
Document and Image Security and Digital Watermarking
Digital watermarking enables corporations and brand owners to embed a unique digital ID into confidential documents and digital images. For instance, a unique digital watermark can be easily embedded into each copy of a confidential document as they are being created and distributed. The data contained in the watermark can include who the recipients are of each copy so that any information that is inadvertently or intentionally leaked out is easily traced back to the source. Finally, watermark detectors can be included in various printers, scanners and other devices to check for watermarks in confidential documents that someone is attempting to copy.
Effective document and image security helps companies
Identify each copy of a confidential document and/or image with a unique digital identity.
Trace back to the source of leaks if sensitive materials are distributed intentionally or inadvertently.
Filter documents being uploaded to the web or forwarded in email to quickly identify confidential materials and stop distribution.
Prevent the copying of confidential documents on copiers and/or scanners.
Authentication of Content and Objects (includes Government IDs)
The impact of counterfeiting is significant, both in terms of lost revenue for businesses and fraud to the consumer, which can even endanger citizens in the case of counterfeit pharmaceuticals. When used as part of a linked and layered security approach, can provide a strong and effective deterrence to counterfeiting and help to solve this costly and challenging problem.
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
Effective authentication of content, IDs and objects helps companies
Reliably authenticate documents, objects and personal IDs at points of inspection.
Ensure that shipments travel their intended route and arrive at the proper destination.
Immediately identify possible tampering or counterfeiting when the watermark is absent.
11. Broadcast Monitoring
Over the last few years, the number of television and radio channels delivering content has notably expanded. And the amount of content flowing through these media vehicles continues to grow exponentially.
Digital watermarking helps content owners and copyright holders to-
Estimate the accurate range of media effects.
Approve and verify content transmission and application.
Determine contractual compliance.
Immediately identify new sales opportunities.
Identify potential misappropriation of assets.
Communicate content rights and intent.
Digital watermarking helps broadcasters and agencies to-
Authenticate bonds and invoices for eventual exactness and responsibility.
Diminish in-flight incongruities by refining media stewardship.
Digital watermarking helps key broadcasters and networks to-
Electronically verify affidavits/invoices.
Replace electronic or manual affidavits/invoices.
Compare schedules versus detections for faster invoice development.
Report or electronically transmit available affidavit/invoice databases.
FORENSIC SCIENCE PAPER No.7: Criminalistics and Forensic Physics MODULE No.34: Digital Watermarking
12. Summary
The objective of watermarks in paper is, essentially identifying the paper as a signature of the manufacturer or as a security measure to avoid forgery of important documents.
Physical steganography has been in use since ancient times and included invisible ink, Morse code on knitting yarn which was then made into garments, microdots, messages on the back of postage stamps and more.
Digital watermarking enables corporations and brand owners to embed a unique digital ID into confidential documents and digital images.
