A method of inspecting a mask, where a structure on the mask is optically imaged at a resolution specified by a criteria set including at least one of a method by which the structure was formed, a tolerance, and a structure type, to produce an optical image. The optical image is compared to a baseline image, and the differences between the optical image and the baseline image are identified. The differences are compared to a threshold value, and any differences that exceed the threshold value are flagged as defects.