1. A method for inspecting a wafer including a multiplicity of dies, the method comprising: aligning at least three images of identical portions of said wafer, thereby to provide at least three mutually aligned images, including adding smear to at least one of said images so as to generate an identical amount of smear in said at least three mutually aligned images; combining said at least three images having identical amounts of smear into a reference; and inspecting each of a plurality of images of a corresponding plurality of portions of a wafer to be inspected, relative to said reference.