The robustness of hollow CAPTCHAs. Gao, H., Wang, W., Qi, J., Wang, X., Liu, X., & Yan, J. In Proceedings of ACM Conference on Computer and Communications Security, pages 1075-1086, 2013.
The robustness of hollow CAPTCHAs [link]Paper  bibtex   
@inproceedings{ dblp2061203,
  title = {The robustness of hollow CAPTCHAs},
  author = {Haichang Gao and Wei Wang and Jiao Qi and Xuqin Wang and Xiyang Liu and Jeff Yan},
  author_short = {Gao, H. and Wang, W. and Qi, J. and Wang, X. and Liu, X. and Yan, J.},
  bibtype = {inproceedings},
  type = {inproceedings},
  year = {2013},
  key = {dblp2061203},
  id = {dblp2061203},
  biburl = {http://www.dblp.org/rec/bibtex/conf/ccs/GaoWQWLY13},
  url = {http://doi.acm.org/10.1145/2508859.2516732},
  conference = {ACM Conference on Computer and Communications Security},
  pages = {1075-1086},
  text = {ACM Conference on Computer and Communications Security 2013:1075-1086},
  booktitle = {Proceedings of ACM Conference on Computer and Communications Security}
}

Downloads: 0