Public Watermarking for Digital Images

Based on the coherence among neighborhood pixels, a public method to embed watermark into spatial domain of an image is proposed. Some pixels and their neighborhood are randomly selected using a secret key, and pixels in each neighborhood are sorted. Then, a bit of the watermark is embedded by adjusting the relation between the selected pixel and other neighborhood pixels. For improving robustness, the watermark is embedded repeatedly. Experimental results show that the proposed technique is robust to common image processing operation. Especially, the extracted watermark is still recognizable when the JPEG compression ratio reaches 1:13.