  We introduce photon theory following the same principles as for introduction
of the quantum theory of a single particle, using a C*-algebraic approach based
on covariance systems. The basic symmetries are additivity of the fields and
additivity of test functions. We write down in explicit form a state of this
covariance system. It turns out to reproduce the traditional Fock
representation of the free photon field, with a Lorentz invariant vacuum.
Properties of smeared-out photons are discussed.
