Test-samples are necessary for the development of emerging imaging approaches such as optoacoustics (OA); these can be used to benchmark new labeling agents and instrumentation, or to characterize image analysis algorithms or the inversion required to form the three-dimensional reconstructions. Alginate beads (AlBes) loaded with labeled mammalian or bacterial cells provide a method of creating defined structures of controllable size and photophysical characteristics and are well-suited for both in vitro and in vivo use. Here we describe a simple and rapid method for efficient and reproducible production of AlBes with specific characteristics and show three example applications with multispectral OA tomography imaging. We show the advantage of AlBes for studying and eventually improving photo-switching OA imaging approaches. As highly defined, homogeneous, quasi point-like signal sources, AlBes might hold similar advantages for studying other agents, light-fluence models, or the impact of detection geometries on correct image formation in the near future.