In this paper, we demonstrated the feasibility of embedding unperceivable code sequence by modulating dot gains through laser intensity modulation for halftone images. From a communication systems point of view, a printer and a document scanner form the physical layer of a communication channel, where information can be hidden in halftone images and reliably transmitted and extracted. In the proposed approach, we will leverage our previous results in embedding unperceivable banding signals to halftone images and develop an integrated embedding and detection algorithm to embed and extract information with high payload capacity. Specifically, we will characterize the embedding capacity and detection rate associated with the proposed algorithm. Preliminary experimental results will be presented.