###### Abstract  
In the past decade, rapid development in digital communication has led to prevalent use of digital images. More importantly, confidentiality issues have also come up recently due to the increase in digital image transmission across the Internet. Therefore, it is necessary to provide high imperceptibility and security to digitally transmitted images. In this paper, a novel blind digital image watermarking scheme is introduced tackling secured transmission of digital images, which provides a higher quality regarding both imperceptibility and robustness parameters. A block based hybrid IWT- SVD transform is implemented for robust transmission of digital images. To ensure high watermark security, the watermark is encrypted using a Pseudo random key which is generated adaptively from cover and watermark images. An encrypted watermark is embedded in randomly selected low entropy blocks to increase the security as well as imperceptibility. Embedding positions within the block are identified adaptively using a Blum-Blum-Shub Pseudo random generator. To ensure higher visual quality, Initial Scaling Factor (ISF) is chosen adaptively from a cover image using image range characteristics. ISF can be optimized using Nature Inspired Optimization (NIO) techniques for higher imperceptibility and robustness. Specifically, the ISF parameter is optimized by using three well-known and novel NIO-based algorithms such as Genetic Algorithms (GA), Artificial Bee Colony (ABC), and Firefly Optimization algorithm. Experiments were conducted for the proposed scheme in terms of imperceptibility, robustness, security, embedding rate, and computational time. Experimental results support higher effectiveness of the proposed scheme. Furthermore, performance comparison has been done with some of the existing state-of-the-art schemes which substantiates the improved performance of the proposed scheme. IWT-SVD; digital image watermarking; adaptive embedding; adaptive scaling factor; pseudo random key; firefly; GA; ABC +
Footnote †: journal: Computer Science and Engineering  
0000-0001-9993-3899]C. O.  
processing attacks, and they are more suitable for secured transmission [6]. In an efficient watermarking scheme, characteristics such as imperceptibility, robustness, and embedding rate play an instrumental role [7]. In particular, imperceptibility is defined as the visual quality of cover and watermarked images, and, ideally, both should be the same. A DIW scheme is considered robust, and provided original and extracted watermarks are almost similar even under attacks. Embedding rate is the ratio between the area of watermark (in bits) and the area of the cover image (in pixels) [8]. However, it is challenging to satisfy these characteristics at the same time and they are always a trade-off. In the last few years, researchers have suggested various schemes to balance this trade-off. One of the prominent solutions is to choose a strong scaling factor (\(\alpha\)) for embedding the watermark. Nature Inspired Optimization (NIO) algorithms have become a very promising scheme to address this issue. Specifically, an effective fitness function can assist in generating a strong scaling factor [9]. However, it is still a challenge to achieve an optimal design for the objective function due to the inherent complex nature of the problem being involved. Watermark security is another important characteristic of watermarking. It is important to protect secret data during its transmission through the internet. To ensure the security of the information, the majority of the researchers have proposed Principle Component (PC) or Singular Value (SV) insertion, the use of hashing techniques, and encryption approaches, but they are less secure approaches. Nowadays, encryption is the most popular security approach [10]. Chaotic maps are often used for encryption, but it has limitations of hyper tuning issues. Therefore, there is a need to develop a strong encryption approach.