  It is argued that large scale cosmic magnetic field could be generated in the
primeval plasma slightly before hydrogen recombination. Non-zero vorticity,
necessary for that, might be created by the photon diffusion in the second
order in the temperature fluctuations. The resulting seed fields at galactic
scale would be only 4 orders of magnitude smaller than the observed ones and
with a mild galactic dynamo amplifying the seed fields by the factor $\sim
10^4$ an existence of coherent magnetic fields in galaxies may be explained.
