Digital Watermarking and its Types

Digital watermarking has emerged as an indispensable technique for protecting intellectual property and asserting copyright in the digital age. With the internet enabling rapid sharing and duplication of digital media, it has become extremely important to have persistent content protection mechanisms that survive processing and distribution.

Digital watermarking provides such a robust solution and has become a crucial tool for content security. This blog provides an in-depth overview of the importance of digital watermarking techniques and applications.

What is Digital Watermarking?

Digital watermarking involves embedding information like identifiers, logos or patterns into digital content through subtle, imperceptible modifications. The embedded watermarks enable copyright protection, usage tracking, authentication and other security applications.

Specialised algorithms are used to embed robust watermarks that can later be extracted to assert ownership or trace misuse. Key techniques include frequency-domain transforms, perceptual analysis and spread spectrum.

Types of Digital Watermarking

There are several ways to classify digital watermarks based on various parameters:

Visible vs Invisible Watermarks

• Visible Watermarks

Visible watermarks like logos and text are intentionally perceptible. They are commonly used for copyright protection in media like images, videos and documents.

Visible watermarks typically contain logos, text, signatures or other graphics overlaid on the content. They visually deter unauthorised use but can be intrusive and removable.

• Invisible Watermarks

Invisible watermarks are imperceptible and embedded robustly for transparency. They are used when the watermark needs to be robust and not alter the viewing experience.

Invisible watermarks are widely used for applications like broadcast monitoring, transaction tracking, etc, where transparency is required. Used for tracking but vulnerable if the algorithm is known.

Fragile vs Robust Watermarks

• Fragile Watermarks

Fragile watermarks are easily corrupted by any small change made to the host content. Even minor manipulations like lossy compression can destroy them.

• Robust Watermarks

Robust watermarks are resistant to common signal-processing operations like compression, filtering, cropping, etc. They are difficult to remove or disable without significantly degrading quality.

Fragile watermarks are used to detect unauthorised tampering or manipulation of data. Strong watermarks are used for copyright protection and tracking where durability is required.

Public vs Private Watermarks

• Public Watermarks

Public watermarks use public keys and algorithms that are known to the public. They offer relatively weaker security since anyone can extract or manipulate them if they know the algorithm.

• Private Watermarks

Private watermarks use secret keys and proprietary algorithms. They are more secure against unauthorised detection and tampering by third parties who don't have knowledge of the keys and algorithms.

However, private watermarks can also be removed by the content owners themselves.

Spatial vs Frequency Domain Watermarking

• Spatial Domain Watermarking

Spatial domain watermarking directly modifies pixel values of the host image to embed the watermark payload. This technique is simpler to understand and implement. However, it provides lower robustness compared to frequency domain techniques.

• Frequency Domain Watermarking

Frequency domain watermarking first transforms the host signal into the frequency domain using transforms like DFT, DCT, DWT, etc., before embedding the watermark in transformed frequency coefficients.

It provides better imperceptibility and higher robustness but has higher complexity.

How Do Digital Watermarks Work?

The process of watermarking involves three main steps:

Watermark Generation

The first step is to generate the watermark containing the information to be embedded. The watermark is generated based on application requirements like robustness, security, payload size, etc.

Random sequences, noise patterns and codes are commonly used to generate watermarks.

Additional keys or passwords may be used to make the watermark generation process more secure. The length and structure of the generated watermark depend on the media, algorithm and desired robustness.

Watermark Embedding

The watermark is then embedded into the original digital media using an embedding algorithm. The algorithm makes subtle modifications to embed the watermark such that it is robust and imperceptible.

Embedding can be done in the spatial or frequency domain. Perceptual masking techniques are used to ensure the changes are below the perceptible threshold. Various transforms like DCT, FFT, SVD, etc. are used.

The embedding can be generalised, content-independent or content-based for optimal results. Key-based techniques provide additional security against removal. The output is the watermarked media.

Watermark Extraction/Detection

The watermark extraction algorithm processes the watermarked content to detect and extract the watermark. The algorithm is designed specifically to counter transformations like compression, noise, filtering, etc.

It may require the original unwatermarked content or additional keys used in embedding. Blind techniques extract watermarks without needing the original.

The extracted watermark is then checked against the original watermark bits to see if they match. Any changes made to the watermarked content should be reflected in the extracted watermark.

Applications of Digital Watermarking

Some major applications of digital watermarking include:

• Copyright Protection

Watermarking provides persistent proof of ownership that survives distribution and processing. It enables tracking down unauthorised usage like piracy. Serving as a digital rights management tool.

• Broadcast Monitoring

TV broadcasters embed unique station/program watermarks into distributed video content. Helps monitor airing across channels/networks to ensure licensed usage.

• Transaction Tracking

Watermarks encoding transaction details like customer ID enable tracing distribution history and leaks of media. Used for video-on-demand, online magazines, etc.

• Content Authentication

Fragile watermarks detect manipulations of medical digital image watermarking, legal documents, etc. Provides assurance of integrity and authenticity.

• Device Fingerprinting

Watermarks fingerprinting production batches, devices, etc., enable tracing origins of pirated copies, counterfeit products, etc., back to the source.

• Covert Communication

Watermarks can transmit secret messages in restricted environments like prisons. It can also encode timestamps, GPS data, etc., for forensic tracking.

Advantages of Digital Watermarking

Some key benefits and strengths of using digital watermarking technology:

• Provides persistent and robust copyright protection that survives distribution and processing
• Imperceptible watermarks do not compromise media quality or viewing experience
• Allows identifying the source of unauthorised distribution by extracting watermark
• Enables tracing leaked documents or data back to the original source device/user
• Can track and monitor usage and distribution history of digital content
• Fragile watermarks detect malicious tampering or alterations to files
• Hard to fully remove the watermark without significantly degrading the host signal quality
• Watermark can encode additional forensic information like timestamps, GPS locations, etc.
• Does not increase file size significantly compared to embedded payload
• Available both as a visible deterrent and hidden tracking mechanism

Watermarking has stood the test of time as an effective digital rights management tool. It provides strong circumstantial evidence for copyright claims in case of infringement. The ability to uniquely fingerprint copies deters large-scale piracy operations.

For sensitive documents, watermarks present a last line of defence that can help trace leaks even if the content is made public.

Limitations of Digital Watermarking

Some disadvantages of digital watermarking:

• Visible watermarks can be distracting and intrusive
• Susceptible to removal attacks like cropping, compression, etc.
• Requires additional embedding and extraction computational steps
• Not completely tamper-proof against highly skilled adversaries
• Needs a careful tradeoff between robustness and perceptibility
• Security depends on the secrecy of keys and algorithms
• It is not very effective for analogue printouts or handwritten documents

Integrating Watermarking in Secure Collaboration

Digital watermarking can be integrated into secure collaboration and document-sharing solutions to enhance data security.

• Visible watermarks deter leakage by employees or external parties
• Fragile watermarks detect alterations in shared documents
• Tracking watermarks trace data exfiltration attempts
• Automate embedding workflows for ease of use by employees
• Analyse watermarks to identify breach sources after incidents
• Layer with encryption and access controls for defence-in-depth

Companies can leverage watermarking capabilities as an additional security control measure on top of existing collaboration protections like antivirus, firewalls, intrusion detection, etc.

Watermarking strengths like tamper evidence, non-repudiation and fingerprinting directly address data leakage and theft risks in digital collaboration.

Recent Innovations in Watermarking

Some recent advancements in digital watermarking:

• Reversible Watermarking - The Watermark can be removed to restore the original for medical/military use cases.
• Deep Learning and AI - Neural networks are used to synthesise watermarks and find optimal adaptivity.
• Encrypted Watermarking - Watermark embedding and extraction are done in the encrypted domain for additional security.
• 3D mesh Watermarking - Robust techniques to watermark 3D printed objects and CAD models.
• Video Watermarking - Frame-by-frame watermarking resilient to video editing attacks.
• Quantum Watermarking - Exploiting quantum physical properties to create more robust watermarks.
• Blockchain Watermarking - Combining blockchain timestamping and hashing for more trust and non-repudiation.

Conclusion

Digital watermarking provides an efficient means to protect intellectual property and enforce copyrights in the digital world. Imperceptible robust watermarks enable persistent content tracking and rights management without affecting quality and usability.

With the increasing importance of data authenticity and growing instances of deep fakes, advanced digital watermarking techniques can play a critical role in media security and verifying authenticity.

Instasafe provides Multi-Factor Authentication to secure access and prevent unauthorised use of files.

Combining Instasafe's access controls with digital watermarking provides robust 360-degree protection for intellectual property and digital assets from leakage and misuse.

FAQs

1. What is the digital watermark process?

The digital watermark process involves generating the watermark, embedding it into content imperceptibly, and then detecting and extracting it to verify authenticity.

2. What are the applications of digital watermarking?

Digital watermarking applications include copyright protection, broadcast monitoring, transaction tracking, tampering detection, and device fingerprinting.

3. What is a watermark example?

A common watermark example is embedding an organisation's logo or ID into images to identify the origin and detect unauthorised use.