  The Fractional Fourier Transform (FRFT) has been playing a unique and
increasingly important role in signal and image processing. In this letter, we
investigate the property of frequency shift in two-dimensional FRFT (2D-FRFT)
domain. It is shown that the magnitude of image reconstruction from phase
information is frequency shift-invariant in 2D-FRFT domain, enhancing the
robustness of image encryption, an important multimedia security task.
Experiments are conducted to demonstrate the effectiveness of this property
against the frequency shift attack, improving the robustness of image
encryption.
