We describe a new method for imaging O2 dynamics on heterogeneous biotic and abiotic surfaces using optical nanosensors. The method can overcome limitations of commonly used optodes or microsensors. To show the potential of the method, the O2 dynamics on the surface of living corals were studied. Small coral fragments were spray-painted with O2 sensor nanoparticles using a conventional airbrush and O2 imaging was done with a simple SLR camera setup. Good coverage of the coral surface was achieved without significantly compromising the coral wellbeing as shown by measuring photosynthetic activity of the photosymbionts at different light levels. The method enabled analysis of spatial heterogeneities in O2 concentration over the coral surface linked to different tissue types. Oxygenic photosynthesis and O2 consumption could be followed at a temporal resolution of <10s.