This paper presents a reliable digital watermarking technique that provides high imperceptibility and robustness for copyright protection using an optimal discrete cosine transform (DCT) psychovisual threshold. An embedding process in this watermarking technique utilizes certain frequency regions of DCT, such that insertion of watermark bits causes the least image distortion. Thus, the optimal psychovisual threshold is determined to embed the watermark in the host image for the best image quality. During the insertion of watermark bits into the certain frequencies of the image, watermark bits are not directly inserted into the frequency coefficient; rather, the certain coefficients are modified based on some rules to construct the watermarked image. The embedding frequencies are determined by using modified entropy finding large redundant areas. Furthermore, the watermark is scrambled before embedding to provide an additional security. In order to verify the proposed technique, our technique is tested under several signal processing and geometric attacks. The experimental results show that our technique achieves higher invisibility and robustness than the existing schemes. The watermark extraction produces high image quality after different types of attacks.

Digital images can be easily copied or manipulated by irresponsible persons. The right property needs to be secured and protected from illegal copies and piracy. Digital watermarking is one of the solutions to protect the intellectual property of digital images. This paper proposed the adaptive scaling factor based on selected DWT-DCT coefficients of its image content. The adaptive scaling factor was generated based on the role of selected DWT-DCT coefficients against the average value of DWT-DCT coefficients. The watermark image was embedded by using a proposed set of rules that consider the adaptive scaling factor. The experimental results showed that the proposed scheme achieved high PSNR value of 47dB, SSIM value of about 0.987 and an embedded watermark resistance to several attacks in the watermarked image.