1. An improved system for real-time scene text recognition;Yang,2015
2. Unconstrained handwritten Devanagari character recognition using convolutional neural networks;Mehrotra,2013
3. Designing human friendly human interaction proofs (hips);Chellapilla,2005
4. Text-based CAPTCHA strengths and weaknesses;Bursztein,2011
5. Deviltyper: a game for CAPTCHA usability evaluation;Ho;Comput. Entertain.,2011