Robust and Fragile Watermarking Scheme Based on DCT and Hash Function for Color Satellite Images

This paper presents a watermarking algorithm to embed robust watermark and fragile authentication data into color satellite images. The aim of this watermarking algorithm is to protect the copyright and image originality. This algorithm doesn´t require the original image in the extraction process and it is a blind algorithm. The algorithm contains two watermarks, one for the copyright and another one for the image authenticity. The first watermark is embedded in the frequency domain using the discrete cosine transform while the second watermark is embedded in the spatial domain which consists of hash functions using MD5 and Hex formats. The fragile watermark is inserted in one row of each one of the RGB channels. The distortion caused by the embedding is assessed using peak signal to noise ratio (PSNR) and similarity structure index measure (SSIM). Robustness against different types of attacks have been assessed using Stirmark and by introducing small modifications to the satellite images. The robust watermarking scheme survived many attacks such as JPEG compression and filtering. The fragile watermark is very sensitive and any small modification to the image can be detected. It was found that embedding in the green channel offers better performance compared to red and blue channels. In addition the embedding in the Y channel offers better robustness against attacks.