An algorithm of digital watermarking based on hyperchaos sequence and the discrete fractional Fourier transform (DFRFT) is proposed. First, the watermark image is scrambled in the spatial domain. The original image and the watermark image are discrete fractional Fourier transformed respectively with different order. Secondly, the watermark image's real part and imaginary part are encrypted by the cipher sequence, which is generated by the hyperchaos sequence. Thirdly, the secondary visual important part of the original image is chosen for embedding into the watermark. At last, the watermark image is obtained after Fourier inversely transformed. The robustness of the watermark image under different attacks such as noise, JPEG compression, the cropping and gaussian low-pass filter is analyzed and the results demonstrate that the embedding scheme has good performance of robustness.

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