We present a model for the QCD structure of hadrons as seen in the dipole picture. The model is based on hot spots -- regions of large gluonic density -- populating the impact parameter space. In our model, the number of hot spots grows with energy and their positions fluctuate event-by-event.
Using this model, we calculate coherent and incoherent photoproduction
of vector mesons off a proton and nuclear targets. We compare our
predictions with current data from HERA, RHIC and the LHC at different
energies. We also present new signatures of saturation effects that could be observed with current and future data.