Radial Spectral Barcode Watermarking for Remote Sensing Images: Extending the Detectable Scale Limits

To extend the scale limits within which a template watermark remains detectable, this paper proposes a template watermarking algorithm for remote sensing images based on a radial spectral barcode (RSB). The RSB is a new geometry of template watermark whose inner and outer boundaries are separated along the radial direction of the discrete Fourier transform magnitude spectrum. In the embedding stage, the spectrum is divided into angular slots, a synchronization sequence generated from the secret key and the watermark are assigned to alternate slots, and the magnitude within the radial interval of each slot is modulated according to its sign. In the detection stage, the angular profile of the received spectrum is computed under a set of geometric hypotheses, the synchronization sequence is located by circular correlation, and the watermark is read from the synchronized profile without correcting the image. The experimental results demonstrate that the proposed method extends the detectable scale interval well beyond that of the ring-template methods while retaining robustness against rotation, translation, cropping, affine transformation, map reprojection, and signal-processing attacks. It outperforms the comparative algorithms in robustness at an equal or higher PSNR, with a low false detection rate.