A machine for distinguishing blisters from checks on the finish of a glass container. The center of each captured object in an array is determined by a controller which determines the object centers in a plurality of adjacent bands. The band having the most object centers is determined and the objects in the band having the most object centers are deleted from the rest of the bands. The control repeatedly determines the band of the rest of the bands having the most object centers and deletes the objects in the band of the rest of the bands having the most object centers from the remainder of the bands until the objects in each band are unique. The maximum separation of objects in each band is defined and checks will be differentiated from blisters based on this separation.