Digital Watermarking [electronic resource] : 6th International Workshop, IWDW 2007 Guangzhou, China, December 3-5, 2007 Proceedings / edited by David Hutchison, Takeo Kanade, Josef Kittler, Jon M. Kleinberg, Friedemann Mattern, John C. Mitchell, Moni Naor, Oscar Nierstrasz, C. Pandu Rangan, Bernhard Steffen, Madhu Sudan, Demetri Terzopoulos, Doug Tygar, Moshe Y. Vardi, Gerhard Weikum, Yun Q. Shi, Hyoung-Joong Kim, Stefan Katzenbeisser