Recently, image watermarking has been used as a tremendous mean for copyright protection of
images andmultimedia as well. This work presents an image watermarking technique for copyright
protection of grayscale images, and is based on the exploitation of the properties of the wavelet
packet decomposition (WPD). Here, the input image is applied to WPD, then, modified trees are
constructed in such a manner to gather WPD coefficients sharing the same spatial locations at
different frequency subbands. The obtained new trees are reorganized in pairs and a differencing
step, between the inter-tree coefficients, is performed. The result is compared to a bi-level threshold.
At the embedding stage, few locations are modified while most of the locations are left unchanged.
To improve the technique security, a content-dependent watermark is implemented and the
threshold is made adaptive to the host under consideration. Simulation results have shown superior
output watermarking quality with a PSNR > 48 dB as well as high robustness against a wide variety
of attacks including moderate-to-severe image compression, filtering, noise addition and enhancementmanipulations.
Moreover, the technique has demonstrated a low computational cost due to the
used approach in selecting the reorganized WPD coefficients.