The term watermarking or “digital watermark” refers to the inclusion of information within a multimedia file, which can subsequently be detected or extracted to draw information on its origin and source.
In other words, the watermark refers to a set of techniques that are intended to hide information in videos, images, audio files, etc.
Thanks to the digital watermark, the information remains secret. To achieve this, we can use various tools such as cryptography and steganography.
Watermark: origins and characteristics
Digital watermarking is a relatively young subject, which has only been studied for a decade.
When was the watermark born?
We cannot deny that images are one of the most important elements to allow Internet users to have a satisfying browsing experience.
Together with the text, the images provide much of the additional information.
Therefore, given the importance of images on the web, it should come as no surprise that over the years many cloud storage services have appeared where you can store your own photographs and social media like Pinterest and Instagram.
The proliferation of online photos hides some negative aspects, especially for photographers who post photos on blogs or on social media.
Given the uncontrollability of the Internet, it could happen that someone appropriates the shots and stores them for his own.
How many photos are “stolen” online? When posting an online photo there is a need to protect it against possible theft attempts.
Watermarking allows you to protect digital photos with a technique from the universe of analogic photography.
The watermark is a kind of signature affixed to your shots to certify the originality and make theft impossible.
The main purpose of watermarking is to protect the originality of a document (both textual and photographic) and make copying impossible. It is similar to the banknote watermark.
These indications leave the document accessible but permanently marked.
They can be latent (hidden inside the file): watermarking can be considered a form of steganography.
Or, they may be obvious to the user of the file (copyright indication superimposed on a digital image).
Watermark: what are the uses?
The digital watermarking technique can be used for several purposes:
- demonstrate the originality of a non-forged document;
- make it clear to all users who the document owner is;
- mark specific characteristics of the document;
- avoid the distribution of unauthorized copies;
- mark the sales path of the document, using a different brand for each buyer.
How to classify watermarks? Watermarks can be classified according to properties, which depend on the purpose with which they were inserted into the document.
Visible or invisible watermarks
A watermark can be visible if it is used to encode information that must be made public to the end user.
The invisible watermark is used when the legitimate owner wants to guarantee the copyrights, thus hiding the trademark in the document.
Private and public watermarks
The private watermarks are those that can be extracted only when their contents are known first and the original unmarked document is owned.
Public watermarks are detectable even if the contents are not known, without the help of the original document. In this case it is easier to identify and remove.
Watermark fragile, semifragile, robust
Fragile watermarks are easily attacked, destroyed and subject to manipulation. They find application in cases where it is desired that a certain information be modified in the passage from the creator to the user and when it must present alterations.
A semi-fragile watermark is easily destructible and modifiable if the inflicted changes are above a certainthreshold set by the user.
A robust watermark is resistant to the most common data transformations: it is used when the ownership of the document must be guaranteed.
Furthermore it is called a robust watermark when it is able to withstand intentional attacks aimed at its removal.
Blind and non-blind watermarks
Non-blind watermarks are more robust and only the owner can demonstrate the presence of the brand.
The watermarks are blind if the original document is not required to verify their presence.
Watermark: Insertion techniques
A watermark can be inserted into an image through different input techniques.
The watermark is incorporated into the transformation coefficients, using the Fourier transform, the cosine discrete and the wavelet transform.
In these cases the image is converted into a matrix showing the numerical values (brightness) of the individual pixels.
One of the invertible transformations is applied to this matrix and some of the transform coefficients are modified, obtaining the insertion of the watermark.
These techniques directly modify the values of the image pixels: they add or subtract the pixel values of the pseudo-random numbers.
To be able to detect the watermark you must have the generating key. This ensures that only authorized users can proceed with the extraction.
Only the values of some pseudocasally chosen pixels are modified: this technique is not particularly robust, especially with respect to counterfeit attempts.
Hybrid techniques can be applied, that is techniques that, while exploiting mathematical transforms, are very effective in adapting the level of insertion of the watermark to the local content of the image.
The NEC method
The NEC method was developed by Cox, Leighton, Kilian and Shamoon and offers greater guarantees from the point of view closely linked to robustness.
The NEC method is part of what are called transform-based techniques, requiring the use of the discrete cosine transform and its inverse.
To ensure the robustness of any watermarking scheme, it is necessary to act on the most perceptually significant components.
This technique is robust and safe with respect to geometric distortions, to the most common signal processing operations and to some more sophisticated intentional attacks.
How to insert a Watermark?
Check out the WooCommerce Watermark plugin! Apply your watermark on your products image. This plugin work perfectly with new and existing product image. You can choose watermark png, jpg or gif from media library or from your local folder.
You can activate this plugin without overwriting the existing images and you can enable or disable the watermark on the images without any problems.
Do you want to receive more information about this plugin? Contact us and you will find a valid answer to all your doubts.
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