  We study the finite temperature behavior of the CPT-even pure-photon sector
of the Standard Model Extension, which is defined by the standard Maxwell
Lagrangian plus the term $(k_F)_{\mu\nu\alpha\beta}F^{\mu\nu}F^{\alpha\beta}$.
The Hamiltonian analysis is performed, from which the degrees of freedom and
constraints of the theory are derived. We have explicitly calculated the
partition function for an arbitrary configuration of the
$(k_F)_{\mu\nu\alpha\beta}$ coefficients, to second order, and we have used it
to obtain the thermodynamic properties of the modified photon sector. We find
the correction to the frequency dependence in Planck's radiation law, and we
identify that the total energy density is adjusted, relative to the standard
scenario, by a global proportionality constant containing the Lorentz-violating
contributions. Nevertheless, the equation of state is not affected by these
modifications.
