One of the main impacts of the JEM-EUSO mission will come from its unprecedented exposure. This feature creates, for the first time in the field, the possibility of studying individual UHECR sources. However, the intrinsic characteristics of the sources and the injection mechanism, as well as the presence of intervening magnetic fields, present challenges to the identification of isolated sources and to the extraction of their relevant spectral information from the data. We discuss here these aspects in a quantitative way and give an overview of what can be achieved in this regard under different astrophysical scenarios.