Cross sections for elastic and proton-dissociative photoproduction of J/ψ mesons are measured with the H1 detector in positron-proton collisions at HERA. The data were collected at ep centre-of-mass energies $\sqrt{s}\approx318~\mathrm{GeV}$ and $\sqrt {s}\approx225 \ \mbox{GeV}$ , corresponding to ...