Donn Morrison Stéphane Marchand-Maillet Eric Bruno TagCaptcha: annotating images with CAPTCHAs. 44-45 2009 KDD Workshop on Human Computation https://doi.org/10.1145/1600150.1600166 conf/kdd/2009hcomp db/conf/kdd/hcomp2009.html#MorrisonMB09