What is a digital watermark?
Every day, hundreds of thousands of digital media files, from images to videos and audio, are produced around the world. And because the Internet is easily accessible to almost everyone, so are these digital media. With the advent of social media, they are shared and reproduced very quickly. More often than not, digital data is stolen or used without proper attribution or identification. How do we protect our data? What are digital watermarks and how do they solve this problem?
What is a watermark?
Did you know that a watermark is an identity document superimposed on an image, video or document to preserve its originality and prevent unauthorized use? Banknote authentication is one of the most important uses of physical watermarks. Watermarks are used to identify genuine money from counterfeits.
What is a digital watermark?
A digital watermark is a mark or, in many cases, a piece of code embedded in digital data (videos, images, or even audio). Digital watermarks, also known as forensic watermarks, may be noticeable or imperceptible and do not alter the information contained in that data.
Digital watermarks protect the copyright of a digital medium and prevent copyright infringement. They are also used to ensure the validity of digital media, because with digital watermarks stolen media can be traced. This way, digital media piracy is reduced and security is improved.
What are the types of digital watermarks?
Digital watermarks can be categorized based on visibility or imperceptibility, robustness, reversibility, ability, and method of embedding. Robustness here refers to the ability of a digital watermark to remain detectable even after undergoing transformations.
1. Visible digital watermarks
Visible digital watermarks, as the name suggests, are watermarks visible to the naked eye. They are also called perceptible digital watermarks. Visible watermarks take the form of logos or transparent images and text affixed to the digital media to be protected. They are also very easy to create. You can watermark your videos using video editors or even add a watermark to an image using Canva.
Visible watermarks can be easy to create, but they are inefficient. For example, a visible digital watermark placed on media such as images or videos can be overlaid or even cropped. Here are some ways to remove a visible watermark from a photo.
2. Invisible digital watermarks
Invisible digital watermarks are watermarks that the human eye cannot see. They are usually pieces of code secretly embedded in digital media to assign ownership and protect copyright. When invisible watermarks are used, it is almost impossible to tell the difference between the watermarked media and its original. Invisible digital watermarks and the information they contain can only be processed by special software using a computer.
3. Fragile and robust watermarks
Brittle watermarks are watermarks that lose their effectiveness when they undergo transformation. When fragile digital watermarks undergo modifications such as resizing or compression, they are destroyed. For this reason, they are used to detect when a digital medium has been tampered with.
Strong digital watermarks are watermarks that can withstand or resist transformation and manipulation. Robust digital watermarks remain intact even during geometric manipulations such as shearing, filtering, resampling or rotation. They are mainly used in digital media ownership protection.
4. Spatial and frequency watermarks
Spatial (domain) watermarking is a digital watermarking technique that involves embedding the digital watermark into the cover image or video pixels. In this technique, the code carrying the information is inserted into the pixels by changing its value or its color intensity. The two main forms of spatial domain watermarking are least significant bit and additive watermarking.
Frequency digital watermarks use the technique of inserting codes into specific frequency bands of a digital medium. When the frequencies of the image are separated, the watermark becomes visible. This technique is more complex than spatial digital watermarking and therefore more effective.
Both techniques are used to create invisible watermarks.
How do digital watermarks work?
Digital watermarks work in two parts: embedding and extraction. The digital watermark is first embedded in the media and extracted if necessary.
As we established above, digital watermarks are markers or codes embedded in digital media to claim ownership and prevent theft. But how does it work?
Digital watermarks use steganography to embed watermarks. Steganography is a technique for hiding data in another medium. It sends and receives secret messages for all to see without detection. For example, using steganography, the pixels or frequency of an image or video can be changed to insert a secret code. Most of the time, media with steganography is encrypted to ensure security.
The main difference between steganography and digital watermark is that the main goal of the former is to keep the secret message hidden from the unsuspecting user whereas in digital watermark the goal is to make the watermark very robust, that is, immune to alterations.
Extracting digital watermarks can be called reversing the digital watermark embedding process. The watermarked digital media is managed by software that decrypts the algorithm used to watermark it and extract the information.
What are the properties of a good digital watermark?
For a watermark to be effective, it must have the following properties:
- It must be sturdy. It should not be easily removed or rendered useless when modified.
- It should be reversible.
- This should not reduce the purpose or the quality of the data. It must be able to protect the content without completely obstructing it.
- It should be secure and hard to break or remove.
Are digital watermarks effective in copyright protection?
Yes quite. Digital watermarks are essential to detect and eliminate data piracy and are used to protect digital assets. The original works of the author are protected and, in case of tampering, the watermarks are used as proof. With the rapid rise of NFTs in our world, digital watermarks are much needed.