A theory is derived to describe the relationship between photonic crystal (PC) label-free imaging resolution and PC resonance spectral linewidth and location. PCs are fabricated and patterned with a resolution standard photomask in order to verify this relationship experimentally. Two distinct linear resolutions of <1 microm and 3.5 microm are demonstrated in orthogonal directions on a single device, where the former is limited by the imaging system optics and the latter is constrained by finite resonant mode propagation. In order to illustrate the utility of improved design control, the spectral response of a PC is optimized for label-free imaging of immobilized DNA capture spots on a microarray.