  In this contribution we present the main results of the investigation about
double parton scattering (DPS) in quasi-real photon-proton interactions. We
show the first evaluation of the DPS cross-section at leading-order for the
four-jet photo-production observed at HERA. To this aim the $\gamma-p$
effective cross section has been computed for the first time. One of the main
outcomes of this analysis is that the DPS contribution is not negligible and
potentially measurable. Furthermore, possible future data could be used to get
new information on the transverse proton structure not accessible in other
processes.
