A novel information-hiding methodology denoted as digital invisible ink is introduced. The proposed approach is inspired by the invisible ink in the real world and can be regarded as an extension of the informed-embedding methodology. Messages hidden in digital contents using digital invisible ink cannot be correctly or clearly revealed unless certain pre-negotiated manipulations have been applied to the marked work. To facilitate such behavior, models and implementations based on both

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... ctrum and quantization-based watermarking approaches are investigated. Finally, benefits and limitations for applying digital invisible ink in common steganography systems and secret communications enabling plausible deniability are discussed.