This thesis explores how the diffraction pattern in the near-field region of a chromium feature edge on a photomask gets altered for three scenarios: First, an analytical study using the Fresnel diffraction integral is performed that investigates what happens when the thin-mask approximation is omitted and the chromium layer is given a thickness. Another analytical study is performed where the edges of a test feature are altered to simulate deviations in the linewidth or a translation of the whole feature, image subtraction is then used to create a difference pattern by subtracting a reference diffraction pattern from the diffraction pattern created by the altered test feature. Lastly, a numerical study using Fourier optics is performed to investigate the effect that introducing four common defects: extrusions, intrusions, dark spots, and pinholes, around the edge will have on the diffraction pattern by subtracting the diffraction pattern from a reference half-plane and again analyzing the resulting difference pattern. Introducing a thickness to the chromium layer alters the diffraction pattern by creating a small crease around the area of the edge in reflective mode, resulting in something similar to a double edge. The high optical density of chromium nullified any effect the thickness had when viewing the system through transmission mode. A linear relation between a change in linewidth or translation of a feature and the peak intensity of the difference pattern is observed that might be used for edge detection. The defect diameter of an extrusion or intrusion seems to correlate in a quadratic way with the peak fringe intensity of the subtracted difference pattern along the x-axis as the defect is fully visible. For a dark spot or pinhole defect being translated away from a chromium edge, the central fringe along the y-axis of the difference pattern follows a sinusoidal curve as it translates further away from the edge. The amplitude of this curve is related to the defect size.