@inproceedings{shirali2011categorizing,
  author    = {Shirali-Shahreza, S. and Shirali-Shahreza, M.},
  title     = {Categorizing {CAPTCHA}},
  booktitle = {Proceedings of the 4th {ACM} Workshop on Artificial Intelligence and Security ({AISec} 2011)},
  address   = {Chicago, IL, USA},
  month     = oct,
  year      = {2011},
  pages     = {107--108},
  doi       = {10.1145/2046684.2046703},
  url       = {https://dl.acm.org/doi/10.1145/2046684.2046703}
}