Digital watermarking based on discrete cosine transform

Ill ABSTRACT MSc Thesis DIGITAL WATERMARKING BASED ON DISCRETE COSINE TRANSFORM Metin ERTURKLER Firat University Graduate School of Natural and Applied Sciences Department of Computer Engineering 2001, Pages :57 Once an image is digitized, it can be easily processed, stored and transferred in network environment. In these processes the main problem is particularly security, such as copyright protections. However during these processes security has not been achieved yet. In this thesis, a watermarking method based on Discrete Cosine Transform, one of the image identification methods is studied and some of its applications are made. A watermark is located into most significant components of image to be robust against malicious attacks and geometric operations. But variations of these components can affect perceptually quality of image. In order to solve this problem, a watermark must be added into low frequency components of images by using Spread Spectrum Communication method. In this process, N x M dimensional Discrete Cosine Transform ofNxM are first computed. Then a watermark are added into the highest magnitude coefficients of any images. Finally, the method given in this study has been used for several images and the results are discussed. Key Words: Digital watermarking, Data Hiding, Copyright Protection, Spread Spectrum Communication.