Digital Watermark

Abstract

Cultural institutions have an increasing need for protection of copyright on the internet. Digital images are easily downloaded and thus need to be protected from misuse. This project will develop a method for provision of protection.

An invisible signal, known as a digital watermark, is a mark placed on a still image. In a project Culture Net Denmark at The Royal library in Copenhagen a method for copyright protection of digital colour images is analysed and implemented.

The signature bits are embedded by modifying the blue channel in the image. A generator that produces random locations in the image, where the signatures bits are embedded, is chosen to prevent any removal of the signature. Specifically, a secret key determines where the signatures bits are embedded in the image.

To extract the signature a user needs to know the secret key.

Furthermore, a method is implemented to retrieve the signature without reference to the original image.

The robustness of the method against possible attacks via geometrical transformation or filtering is analysed.