AprilTags were developed by Professor Edwin Olson of the University of
Michigan.  His Java implementation is available on his web site:
  http://april.eecs.umich.edu.

Olson's Java code was ported to C++ and integrated into the Tekkotsu
framework by Jeffrey Boyland and David Touretzky.

See this Tekkotsu wiki article for additional links and references:
  http://wiki.tekkotsu.org/index.php/AprilTags