The present invention provides a high-precision alignment method, device and code for inspections that compare an inspection image with a reference image and detect defects from their differences. In one embodiment an inspection image and a reference image are divided into multiple regions. An offset is calculated for each pair of sub-images. Out of these multiple offsets, only the offsets with high reliability are used to determine an offset for the entire image. This allows high-precision alignment with little or no dependency on pattern density or shape, differences in luminance between images, and uneven luminance within individual images. Also, detection sensitivity is adjusted as necessary by monitoring alignment precision.