Dynamic visual cryptography is a technique for the encryption of secret visual information in such a way that the decryption is absolutely visual. The secret is encoded into the moire grating using complex computational algorithms, but the decoding can be performed simply by observing oscillating encoded cover image by a naked eye. The law of the oscillations is always preselected before the encoding procedure. However, if the secret image is encoded into the harmonic moire grating and the oscillation of the cover image is performed on the computer screen, the implementation of harmonic oscillations is not possible due to some constrains related with technical characteristics of the digital screen. The main aim of this investigation is to determine near-optimal pair of pitches of the moire grating for the case when oscillations according to a rectangular waveform function are used for image hiding in dynamic visual cryptography.
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