WASET
    Yucel Ugurlu,  Human Interactive E-learning Systems using Head Posture Images.   journal   = {International Journal of Computer and Information Engineering}, [online]. World Academy of Science, Engineering and Technology.
    May 2012, vol. 65(5). 703 - 706
    [viewed 25 April 2024]. Available from: https://publications.waset.org/pdf/16027.