1. A method for inspecting a photo-mask that corresponds to a mask pattern, comprising: receiving an inspection image corresponding to the photo-mask, wherein the inspection image is determined using an optical imaging system; reconstructing an estimated pattern corresponding to the photo-mask at an object plane of the optical imaging system based on the mask pattern, wherein the estimated pattern is determined using an inverse optical calculation in which the inspection image is in an image plane of the optical imaging system; and using the estimated pattern to identify potential defects in the photo-mask, thereby facilitating inspection of the photo-mask.