## 9 Conclusions  
This research introduces a robust forensic watermark method that addresses challenges in the distribution of digital evidence outside cloud environments. It proposes a secure solution for sharing JPEG images within forensic disk images and as stand-alone files for evidence integrity and traceability.  
The adaptive DCT-DWT domain technique preserves the structure of forensic disk images and maintains compatibility with industry standard tools such as FTK and Autopsy. The comprehensive tool compatibility tests confirm that the watermarking process supports full forensic functionality, from file system navigation to timeline analysis. This approach integrates smoothly with existing forensic workflows and allows investigators to continue using familiar tools.  
Quantitative security assessments demonstrate the resistance of the method to multiple attack vectors. The system withstands collusion attacks, with a minimum of eight distinct copies required to degrade the watermark below detection thresholds. Cryptanalytic attacks against the PRNG seed remain computationally intensive and require approximately 252 operations even with knowledge of 60% of previously watermarked blocks. These metrics provide concrete evidence of the security of the approach in real-world forensic scenarios.  
The dual domain watermarking approach demonstrated exceptional performance in diverse datasets. With PSNR values ranging from 46.13 dB to 49.37 dB and BER = 0 versus JPEG compression at quality factors greater than 60, the method balances imperceptibility with robust watermark extraction. The feature-based geometric resynchronisation ensures watermark recovery even after substantial image transformations.  
The watermark applies only to the distribution copies and leaves the original gold copy intact and securely stored to preserve the chain of custody. The embedded recipient identifiers enable precise leak source attribution with identification accuracy above 92%, even under partial parameter compromise scenarios.  
This technique serves law enforcement agencies as a bridge between current evidence management practices and future cloud-based systems. It offers immediate benefits to organisations that lack a comprehensive cloud infrastructure and supports the transition to more secure centralised systems. The system addresses the current reality of digital evidence sharing without disrupting established workflows.  
Although this approach offers robust protection, it does face challenges with extremely degraded images under multiple simultaneous attacks. Future research will explore zero-watermarking methods that eliminate the need for image modification and investigate integration with cloud-based forensic platforms for enhanced security. For forensic practitioners, this technique requires minimal implementation effort with existing tools and can be deployed within current operational time frames. A phased adoption approach that begins with high-sensitivity cases offers the most practical path to implementation.  
This research fills a critical gap in forensic watermarking by providing a practical, immediately applicable solution that balances robust security with operational requirements. The approach marks a significant advancement in the protection of digital evidence and creates new possibilities for secure evidence distribution within the constraints of modern forensic investigations.  
**Author Contributions:** Conceptualisation, B.I.O.; Methodology, B.I.O.; Writing--original draft, B.I.O.; Writing--review & editing, P.L., S.M. and G.R.; Visualisation, B.I.O.; Supervision, P.L., S.M. and G.R. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Data Availability Statement:** Data are contained within the article, and the associated forensic disk image dataset is being prepared for open-source release.  
**Conflicts of Interest:** The authors declare no conflicts of interest.