No Bot Expects the DeepCAPTCHA! Introducing Immutable Adversarial Examples, With Applications to CAPTCHA Generation.
Margarita OsadchyJulio C. Hernandez-CastroStuart J. GibsonOrr DunkelmanDaniel Pérez-CaboPublished in: IEEE Trans. Inf. Forensics Secur. (2017)