Pessimal Print: A Reverse Turing Test. - Allison L. Coates; Richard J. Fateman; Henry S. Baird (ICDAR, 2001)

PessimalPrint: a reverse Turing test. - Henry S. Baird; Allison L. Coates; Richard J. Fateman (Int. J. Document Anal. Recognit., 2003)