Abstract: The binary phase-only filter digital watermarking embeds the phase information of the discrete Fourier transform of an image into the corresponding magnitude for image authentication.In the paper，embedding the BPOF watermark by quantizing the magnitude is studied.Adjusting the quantization steps following the frequencies of the magnitude coefficients，and embedding the watermark into the low frequencies are discussed.Theoretical analysis and experimental results show that，with quantization based watermark embedding，the flexibility，security，watermark imperceptibility and detection performance are improved effectively，while the robustness against JPEG compression is enhanced at a certain degree.