Digital watermarking for copyright protection

This work presents the design and implementation of a digital watermarking system used for the copyright protection of digital images. This watermarking system involves both the visible and invisible watermarking or bitmap images. In the instance where invisible watermarking takes place, it is important to maintain the integrity or image quality of the image being watermarked. This implies that the image should not be subjected to more than the acceptable degradation level which is specified in terms of the peak signal to noise ratio (PSNR). An acceptable degradation level was defined to be a PSNR value greater than 35 dB. Running the secure hash algorithm (SHA-1) hash function over the encrypted watermark ensures the integrity of the watermark. Secrecy is provided by means of symmetric key encryption. This is achieved by the utilization of the AES-Rijndael algorithm. Embedding and reconstruction of the watermark is based on the discrete cosine transform (DCT). This method ensures that the watermark is cryptographically secure when embedded in an image. Watermark detection, reconstruction and tamper indication are features of this design.