Optimized gray-scale image watermarking using DWT–SVD and Firefly Algorithm

•In this paper, image watermarking is implemented using DWT–SVD domain.•The Firefly Algorithm is used to implement image watermarking for the first time.•We demonstrate successful use of multiple scaling factors to achieve best results.•Robustness study indicates embedding algorithm is robust against image operations.•Watermark extraction from signed and attacked images is found to be well optimized.

This paper presents an optimized watermarking scheme based on the discrete wavelet transform (DWT) and singular value decomposition (SVD). The singular values of a binary watermark are embedded in singular values of the LL3 sub-band coefficients of the host image by making use of multiple scaling factors (MSFs). The MSFs are optimized using a newly proposed Firefly Algorithm having an objective function which is a linear combination of imperceptibility and robustness. The PSNR values indicate that the visual quality of the signed and attacked images is good. The embedding algorithm is robust against common image processing operations. It is concluded that the embedding and extraction of the proposed algorithm is well optimized, robust and show an improvement over other similar reported methods.