@inproceedings{shirali2007collage,
  author    = {M. Shirali-Shahreza and S. Shirali-Shahreza},
  title     = {Collage CAPTCHA},
  booktitle = {Proceedings of the 20th IEEE International Symposium Signal Processing and Application (ISSPA 2007)},
  address   = {Sharjah, United Arab Emirates},
  month     = feb,
  year      = {2007},
  pages     = {1--4},
  doi       = {10.1109/ISSPA.2007.4555329},
  url       = {https://doi.org/10.1109/ISSPA.2007.4555329}
}