Nidal F. Shilbayeh and  Belal AbuHaija and  Zainab N. Al-Qudsy,  A Robust Hybrid Blind Digital Image Watermarking System Using Discrete Wavelet Transform and Contourlet Transform .   journal   = {International Journal of Computer and Information Engineering}, [online]. World Academy of Science, Engineering and Technology.
    March 2017, vol. 123(3). 407 - 413
    [viewed 30 May 2020]. Available from: https://publications.waset.org/pdf/10006912.