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Figure 1.  The schematic configuration of optical image watermarking based on OAM holography. (a) The watermark preprocessing process. (b) The watermark embedding system. (c) OAM-watermark hologram recovery system. (d) The optical reconstruction method.

Figure 2.  The experimental decryption process: (a) the optical setup, (b) the experimental results with different key beam (Key₁ = 0 and −2) and the scrambling time (Key₂ = m and m – 1).

Figure 3.  (a) The processes of adding the interference image. (b) The comparison of the captured results without and with the interfering image.

Figure 4.  (a) The PSNR with different embedding levels (p), and the sub-watermark number (K). (b) Histograms of the original host image and different watermarked host images. (c) The correlation coefficient (CC) with different embedding levels.

Figure 5.  The experimental results of different attack tests, including Gaussian noise, Poisson noise, salt-pepper noise, JPEG compression attacks, Gaussian low-pass filtering, cropping, and rotation.

Figure 6.  Histogram and CC experimental results for embedding the cryptographic OAM hologram into different components.