Nowadays, color screen, powerful computing processors, and high speed data communication protocols are supported by more and more mobile phones. Through these new technologies, it is possible for mobile phone users to download, view, and even edit images on their mobile phones. However, this poses a new challenge for mobile software developers if they want to allow several users to edit on the same image. Traditional methods (e.g., white board method) cannot be used under mobile environment due to its high communication cost. In this paper, we propose a cooperative editing tool based on an asynchronous method to greatly save the communication cost. The tool is successfully used as a plug-in in our Mobile Information and Resource Exchange System (MIRES).