New image blind watermarking method based on two-dimensional discrete cosine transform

•The size relationship between the selected middle frequency coefficients of 2D-DCT is used to embed and extract watermark information.•Comparing with traditional algorithms which are based on DCT, the watermark capacity of this algorithm is larger.•The proposed algorithm is a blind watermarking algorithm, and the original data or original watermark is not needed in the process of watermark extraction.•Comparing with other relevant algorithm, the proposed algorithm has higher invisibility and stronger robustness, which is suitable for digital image copyright protection.