Gwo-Chin Tai Long-Wen Chang Visual Cryptography for Digital Watermarking in Still Images. 50-57 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3332&spage=50 2004 conf/pcm/2004-2 PCM (2) db/conf/pcm/pcm2004-2.html#TaiC04