This book constitutes the refereed proceedings of the 4th International Workshop on Digital Watermarking Secure Data Management, IWDW 2005, held in Siena, Italy in September 2005.

The 31 revised full papers presented were carefully reviewed and selected from 74 submissions. The papers are organized in topical sections on steganography and steganalysis, fingerprinting, watermarking, attacks, watermarking security, watermarking of unconventional media, channel coding and watermarking, theory, and applications.