  We discuss the electromagnetic corrections to the pion-nucleon scattering
lengths generated by minimal e. m. coupling from a knowledge of the low energy
expansion of the pion-nucleon elastic scattering amplitude as well as from the
nucleon and delta pole terms, all a consequence of purely strong interactions.
We assume the heavy baryon limit; the e.m. and axial form factors and the
masses are used with their empirical values, such that there is no free
parameter. The different terms have a clear physical and intuitive origin. In
particular, a large isospin breaking contribution to the isoscalar term appears
for the elastic charged-pion scattering lengths. We attempt a comparison to the
results from chiral effective field theory (EFT) with a physical interpretation
of the empirical constants in that approach. The results are applied to the
energy shift and width of pionic hydrogen.
