1. A device for inspecting a plate-shaped product having a pattern area through which inspection rays can pass and a background area, and for detecting and evaluating flaws in said background area, said flaws corresponding to portions of said background area which allow said inspection rays to pass therethrough, said device comprising: (a) holding means for holding said product to be inspected; (b) an inspection ray source providing said inspection rays to a first side of said product; (c) an imaging camera arranged so as to obtain an image of a second side of said product illuminated by said inspection ray source, said image including a pattern portion corresponding to said pattern area and a background portion corresponding to said background area; (d) masking means for masking said pattern portion of said image to prevent inspection rays that pass through said pattern area from appearing in a masked image of said product while permitting inspection rays that pass through said background area to appear as spots in said masked image, said spots in said masked image corresponding to said flaws in said background area of said product; (e) means for detecting a size of each of said spots in said masked image and a distance of each of said spot from said pattern portion; (f) means for defining thresholds corresponding to an allowable maximum limit of a size of each of said spots, said thresholds being defined such that a value of a threshold associated each spot decreases as said distance of that spot from said pattern portion increases; and (g) means for comparing said actual size of each of said spots to one of said thresholds to determine whether said size of said spot exceeds a maximum limit so as to cause said product to be rejected.