In this paper we demonstrate the possibility of backward radiation from a negative permittivity planar (slab) waveguide. Furthermore, we show that backward radiation can be used to achieve sub-wavelength imaging of a point source placed close to such a slab or to a periodic layered system of slabs. Finally, we demonstrate backward-radiation-based imaging in the case of realistic materials operating in the THz regime, such as polaritonic alkali-halide systems.