Auger depth profiling was used to determine the local film thickness of a thin anodic oxide grown on a polycrystalline Ti substrate. The oxide thickness was studied as a function of substrate crystallography and final growth voltage. These results were related to local photocurrent measurements obtained using photoelectrochemical microscopy. Variations in the film thickness are too small to account for the non-uniform photocurrent response. The non-uniform photoresponse is instead attributed to variations in the defect density of the oxide.