# Image Watermarking between Conventional and Learning-Based Techniques: A Literature Review
## 1 Introduction  
Digital media in this era has become an integral component of every individual's daily life. Large amounts of data are stored and exchanged easily at an incredible speed [1] due to the current technological advancements that provide environments for data sharing and a vast amount of storage space. However, there are many concerns about the illegal piracy of copyrighted media. This issue gave rise to the concept of digital watermarking. Since the 1990s, it has become a new research direction and is attracting significant interest in the scientific community. Watermarking is considered a relatively young discipline and appears to be a suitably efficient solution for different security fields, such as copyright protection and authentication [2]. Figure 1 shows the chronological development of embedding operations in watermarking. Digital image watermarking is a technique in which a secret mark is concealed in the host multimedia to create the watermarked image, which is then communicated through  
Figure 1: Watermarking operations chronology. a physical transmission channel. At this point, digital content may easily be retrieved, reproduced, and distributed illegally. Later on, the watermark is detected or extracted from the recovered image, which aims to confirming the ownership and guarantee tamper resistance. Watermarking schemes are divided into blind and non-blind based on the extraction requirements [3]. In blind watermarking, the extraction is achieved from the received container, whereas in non-blind watermarking, the original container is required for extraction. For the purpose of preserving the content security of digital media, several techniques have been regarded as effective and practical techniques of copyright protection, such as cryptography and steganography [4]. The main goal of cryptography is to scramble the message, making it unintelligible and not subject to encryption or interpretation, in order to achieve the major security components. However, once the secret data have been cracked in some way, it will be entirely controlled by the attacker, and the original user will not be able to track it, especially if it has been cloned. Steganography, on the other hand, is considered as a one-to-one communication method based on invisibly hiding the secret data from unauthorized users by putting them into the cover media, so that only the sender and the intended receiver can identify the delivered message,; therefore, it can be used as an alternative tool for privacy and security. Yet, this technology is still not robust against attacks where a malicious manipulation or distribution of data makes the message easily lost and hard to recover. Subsequently, the emergence of digital watermarking technology perfectly solves the shortcomings of the last two defined techniques [5]. It is a technique similar to steganography; however, it overcomes the weaknesses in both cryptography and steganography. The concealed watermark is imperceptible and difficult to remove by unauthorized persons. The embedded watermark can be used to verify ownership if the container is targeted or tampered with [6]. This advantage makes image watermarking appropriate for a variety of applications [7]. In recent times, popular applications of watermarking [8; 9; 10; 11; 12; 13] include 5G communication, Internet of Things (IoT), cyber systems, IP protection, relational databases, 3D images, fingerprinting, e-governance, digital forensics, military, medical, file archiving, hardware protection, secure social data in smart city, secure cloud storage data, e-voting, and remote education. A set of watermarking applications are shown in Figure 2. With the growth and popularity of the Internet, as well as the introduction of numerous live broadcast platforms, all types of pirated videos are flooding online. This seriously violates the rights and interests of owners of video copyrights and prevents the video industry from growing in a healthy way.