A new robust public watermarking algorithm in DCT (discrete cosine transform) domain is presented. Due to good randomness and easy reproducibility of chaos, the watermark is firstly permuted by the hashed chaotic sequence, then a small number of reference points are randomly selected in the middle frequency bands of the DCT domain based on the chaotic sequences, and the batch-type disorder watermark bits are embedded into the neighborhood of every reference point using odd-even quantization. The usefulness of multilevel chaotic keys and privacy of modification to frequency coefficients enhance the security of watermark information. The blind extraction of watermarking information is realized under guaranteeing that a larger capacity and significant binary watermark is hidden. Moreover, a reasonable trade-off between the invisibility and robustness is obtained.