A brief analysis of several common digital watermarking techniques

Digital watermarking technology is an information hiding technology, which can embed copyright information, logo information, image and other information into video, audio, image, text and other carrier images in a visible or invisible way. When embedding invisible watermark information, because the embedded watermark information is lower than the minimum granularity discovery range that the human visual system can bear, on the one hand, it can be used to prove the source of the work as evidence of infringement litigation, on the other hand, it can also achieve the integrity protection of the work by detecting and analyzing the watermark of the digital work.
Common digital watermarking technologies include gray value encryption and position encryption.
1. Gray value encryption
The gray value histogram of an image is essentially a function that represents the relationship between the gray values at all levels of a digital image and their occurrence frequency. It describes the number of pixels with the gray value in the image.
Pixel gray value encryption is to use the gray value disturbing vector (matrix) generated by chaotic mapping to disturb the original image pixel value to achieve the purpose of hiding image information. The gray value encryption is obtained by XOR of two matrices.
2. Location encryption
Position encryption mainly uses the characteristics of non-repetition, unpredictability and extreme sensitivity to initial conditions of chaotic behavior to generate chaotic position disturbance vector or chaotic position scrambling matrix after processing chaotic sequence to change the position of pixels in the original image matrix, so as to achieve the purpose of unreadable image and masking image information.
3. Double-factor encryption method
Because the implementation principle of location encryption is relatively simple, although the watermark image after location encryption has achieved scrambling in visual effect, it cannot change the original image histogram. In this way, it is easy to disclose the statistical information of the watermark image. Therefore, in order to enhance the security, a combination of position encryption and gray value encryption (double factor encryption) is used to encrypt the watermark image. This encryption method can reduce the probability of watermark being cracked when the watermark image is extracted, and ensure the security and confidentiality of the watermark.
From the perspective of watermark encryption, the two-factor encryption mechanism generates two chaotic matrices when encrypting the digital watermark, one for position encryption and the other for grayscale encryption. When the two are combined, the chaotic sequence is unpredictable, so even if the watermark sequence is known, the watermark information cannot be cracked without the key matrix of chaotic encryption. In order to meet the requirements of watermark security, and thus play a better protection of copyright.