Computers beat Humans at Single Character Recognition in Reading based Human Interaction Proofs (HIPs)
IMAGINATION: a robust image-based CAPTCHA generation system
Usability of CAPTCHAs or usability issues in CAPTCHA design
An efficient segmentation algorithm for CAPTCHAs with line cluttering and character warping
Asirra: a CAPTCHA that exploits interest-aligned manual image categorization
Using Machine Learning to Break Visual Human Interaction Proofs (HIPs)