1. A computer-implemented method for determining a disposition of a possible defect in a photo-mask, comprising: receiving a first image of a first region around the possible defect in the photo-mask, wherein the photo-mask corresponds to a target mask pattern; generating, via the computer, a second image based on the first image, wherein the second image includes the first region and a second region surrounding the first region, and wherein the second region is based on the target mask pattern; calculating a simulated mask pattern based on the second image using an inverse optical calculation in which the second image is at an image plane in a model of an optical system and the simulated mask pattern is at an object plane in the model of the optical system; simulating a wafer pattern in a photo-lithographic process based on the simulated mask pattern; and determining the disposition of the possible defect based on the simulated wafer pattern and a target wafer pattern.