Image Watermarking Algorithm Using DWT and DCT

This image watermarking algorithm utilizing Wavelet Transform and Discrete Cosine Transform offers a straightforward implementation process with reasonably effective results. The algorithm embeds watermarks into the frequency domain of images through a multi-stage transformation approach: first applying DWT to decompose the image into sub-bands (LL, LH, HL, HH), then performing DCT on selected sub-bands for watermark insertion. This dual-transformation technique provides protection and authentication for digital images by leveraging advanced digital signal processing methods. The implementation typically involves key functions such as dwt2() for wavelet decomposition, dct2() for frequency transformation, and quantization-based embedding strategies that modify mid-frequency DCT coefficients to balance robustness and imperceptibility. The algorithm demonstrates effective resistance against common attacks like noise addition and image compression through its frequency-domain embedding strategy. Furthermore, the method exhibits good robustness and concealment characteristics, maintaining image quality while ensuring watermark invisibility. The algorithm's strength lies in its hierarchical processing - using DWT for multi-resolution analysis and DCT for energy compaction in selected sub-bands. This combination makes it a viable solution for digital image copyright protection and content authentication applications, particularly suitable for implementations using MATLAB's image processing toolbox or similar computational frameworks.