  We explore the electromagnetic contribution to the charge symmetry breaking
in the octet baryon masses using a subtracted dispersion relation based on the
Cottingham formula. For the proton-neutron mass splitting we report a minor
revision of the recent analysis of Walker-Loud, Carlson and Miller. For the
electromagnetic structure of the hyperons we constrain our analysis, where
possible, by a combination of lattice QCD and SU(3) symmetry breaking
estimates. The results for the baryon mass splittings are found to be
compatible with recent lattice QCD+QED determinations. The uncertainties in the
dispersive analysis are dominated by the lack of knowledge of the hyperon
inelastic structure.
