This book constitutes the refereed proceedings of the 6th International Workshop, IWDW 2007, held in Guangzhou, China, in December 2007. The 24 revised full papers together with 3 invited papers were carefully reviewed and selected from 81 submissions. The papers are organized in topical sections on watermark security; steganalysis; authentication; reversible data hiding; robust watermarking; poster session; theory and methods in watermarking.