The coding efficiency of a still image coder is dominated by the complexity of the encoding algorithm. For the past decade, it was seen that the encoding quality was gradually limited. Hence, the issue of coding speed becomes popular in recent researches. This paper proposes a block-based image coder which is applicable for parallel computing. The proposed coder improves the coding quality of combined significant map coding (CSMC), and shortens the encoding time dramatically. From the simulation results, the proposed method has comparable coding quality against the most well-known coders. The coding quality is not affected by the number of participants, so it is also suitable to be applied in cloud computing. Besides, the proposed block-based image coder preserves the property of high scalability and availability. We conclude that our proposed coder enabled by parallel computing has a great advantage of fitting with the increasing complexity of computation.