The influence of the CAPTCHA types to its solving times. - Darko Brodic; Sanja Petrovska; Milena Jevtic; Zoran N. Milivojevic (MIPRO, 2016)

User-Centric Analysis of the CAPTCHA Response Time: A New Perspective in Artificial Intelligence. - Darko Brodic; Sanja Petrovska; Radmila Jankovic; Alessia Amelio; Ivo R. Draganov (ERCIM News, 2017)

The CAPTCHA Samples Websit. - Alessia Amelio; Darko Brodic; Sanja Petrovska; Radmila Jankovic (ERCIM News, 2018)