NATURE INSPIRED ALGORITHM FOR ENHANCING SECURITY AND ROBUSTNESS IN IMAGE WATERMARKING

Abstract

The rapid growth of digital media and the rising risk of tampering have made digital watermarking a vital tool for content authentication and protection. This study introduces a double watermarking system that integrates hybrid transform methods, intelligent block selection, and chaotic encryption to embed two watermarks into grayscale images while maintaining visual quality and robustness. The Firefly Algorithm (FA) is used to select optimal blocks based on local variance, ensuring watermark insertion with minimal distortion. The first watermark is embedded using Discrete Wavelet Transform (DWT) with Singular Value Decomposition (SVD), which strengthens resistance against geometric attacks. The second watermark is embedded through the Discrete Cosine Transform (DCT), targeting low-frequency components to improve robustness against compression and filtering. To secure the watermark, Lorenz Chaotic Encryption is applied before embedding, making extraction meaningless without the correct decryption key and providing resistance against brute-force attacks. Experiments on 39 grayscale images including natural scenes, textures, and synthetic patterns confirmed the effectiveness of the model. The system achieved a PSNR of 65.94 dB for the first watermark and 63.46 dB for double watermarking, reflecting excellent imperceptibility. The SSIM score of 0.999 indicated near-identical image quality. Robustness was also high, with 94.87% accuracy for the first watermark (DWT-SVD) and 97.76% accuracy for the double watermark (DCT).This work contributes a reliable framework that combines transform-based embedding, block optimization, and chaos encryption, providing a secure and robust solution for digital content protection. In contrast to the previous approach, we use DWT SVD only on blocks that are considered to be textured and DCT on blocked that are smooth and Firefly Algorithm is employed to select the embedding locations and Lorenz chaotic scrambling is applied to the watermark, a, a combination not reported previously.