The imaging behaviors for two kinds of polarized waves found by using a two-dimensional annular photonic crystal flat lens are theoretically investigated. For the TE-polarization, subwavelength imaging due to a negative refraction effect is obtained and the focal length can be adjusted by changing the lens thickness. In contrast, for the TM-polarization, because the resulting optical field distribution behind the slab resembles a triple point source due to the effect of channeling, the light can focus again due to the interference effect. Most importantly, using the proper annular photonic crystal lens, the image of an unpolarized wave point source can be realized. These results show that the negative refraction is not the one and only mechanism of imaging by a photonic crystal lens.