## 2 Brief Overview  
Existing DIW schemes mainly focus on achieving higher imperceptibility, robustness, and embedding rate by embedding the watermark in spatial and spectral domains. The DIW schemes proposed in [11; 12; 13; 14] utilize spatial domain techniques. In general, spatial domain techniques are imperceptible but less robust. Therefore, researchers have also explored hybrid transform watermarking schemes for high imperceptibility and robustness, such as DWT-SVD [15; 16; 17; 18], DWT-DCT [19; 20], RDWT-SVD [21], and IWT-SVD [22; 23]. The schemes proposed in [22; 23] have high imperceptibility but lag behind in robustness, which can be attributed to the trade-off between watermarking characteristics. To balance this trade-off, the scaling factor for watermark embedding and extraction is suggested [11; 12; 13; 16; 18; 20; 23; 24; 25]. However, determining the scaling factor is challenging. In addition to that, using a constant scaling factor may not be effective for all images. Some researchers have offered scaling factor optimization strategies to overcome these problems. Schemes proposed in [15; 17; 21; 22; 26; 27; 28] use NIO algorithms such as MACO, GA, Firefly, ABC, GDPSO and ACO, respectively, for scaling factor optimization. Scaling factor is optimized using QIM in [19] and the fuzzy logic system in [12]. However, the schemes in [22; 26] use optimized scaling factor but are less robust. Adaptive embedding techniques to ensure high imperceptibility and robustness are also suggested [16; 29]. Watermark security is very important for watermark applications such as IoMT, Telemedicine, IoT, Big Data, cloud computing, and blockchain technology. However, watermark security is either overlooked or less focused on in most of the DIW schemes. However, the schemes presented in [12; 15; 17; 21; 22; 26] optimize watermarking characteristics but ignore watermark security. For watermark security, schemes in [16; 27; 28; 29; 30; 31; 32] use entropy, histogram, pseudo random key, DDFA, d-sequence, and GBA, respectively, for adaptively locating embedding blocks, but provide lower security. Similarly, schemes proposedin [11; 14; 18; 20; 30; 31] have high imperceptibility but are less secure. However, the techniques presented in [24; 28; 33] achieve great imperceptibility, robustness, and security at the expense of a large computational cost. Another way of ensuring watermark security is to use cryptographic techniques. An Arnold map is used for watermark security in [19; 28], although the Arnold map has a low iteration value. A chaotic map is used in schemes [13; 23; 34], but a chaotic map has an issue with the hyper tuning parameter. **Motivation and contribution of the proposed scheme:** A study of related watermarking schemes reveals that most of the DIW schemes underestimate watermark security, whereas some have used cryptographic techniques like chaotic and Arnold map, which suffer from the iteration parameter and hyper tuning issues, respectively. In addition to that, the embedding positions in cover image are predetermined in most of the existing schemes, which further dilutes the confidentiality of watermark. In addition, most of the watermarking schemes use a constant scaling factor for embedding. Few schemes suggest optimization of the scaling factor using NIO algorithms to achieve high watermarking characteristics. Choosing a constant initial scaling factor for all image modalities may degrade watermarking characteristics. To address these challenges, a novel DIW scheme is proposed in this paper. The proposed scheme is motivated by [PERSON] and [PERSON] [18], [PERSON] [31], [PERSON] and [PERSON] [32], [PERSON] and [PERSON] [27], and [PERSON] et al. [23]. A contribution of the proposed scheme is as follows:  
1. High Watermark Security: The proposed scheme ensures twofold watermark security by encrypting the watermark and then embedding it in randomly selected positions in transformed cover image blocks. The watermark is partitioned into odd and even position pixel vectors.