Robust and Invisible Image Watermarking for Presentation Slides in E-Learning

Problem of copyright infringement on presentation slides available online continued to increase over the next few years. Digital image watermarking is developed and used to discourage people from violating copyrighted contents in presentation slides. This paper presents a robust and invisible image watermarking method particularly developed for presentation slide in e-learning. By considering the entire area of presentation slide as a color image, the reflectance component from its blue color channel was extracted and used to carry the watermark. The watermark extraction is blindly achieved by predicting the original reflectance component from the guided image filter, and subtracting the result from the watermarked component. The performance of our proposed watermarking method in terms of wPSNR and BCR is evaluated, and compared with the two previous methods. Improved performance in terms of robustness against various attacks was also evaluated and shown.