Self-embedding and restoration algorithms for document watermark

When a document or a sequence of characters is tampered, watermarking should be able to not only detect the tampering but also restore it. Towards this goal, self-embedding is used where the watermark is a copy of the sequence itself. Restoration algorithms for substitution attack are proposed for two variants of self-embedding. These algorithms are analyzed to show where they fail and how to avoid these failures. Strategies to cope with deletion/insertion attacks are also mentioned.