JPEG2000, a successor of JPEG, offers highly scalable image coding as one of its features. This scalable feature and its superior coding performance make it very attractive for transmission over peer-to-peer networks. In this paper, we study two algorithms aimed for different applications. First, we propose a layerbased peer transmission algorithm to achieve the best image quality layer by layer when the image is viewed while downloading. Second, we propose a time-based peer transmission algorithm to minimize transmission time when the image is viewed after downloading. We have built a peer-to-peer networking environment using Pocket PCs, and evaluated the two proposed algorithms using an image transmission prototype implemented by Microsoft .NET framework.