1. A method for detecting an item inside an inspection object the method comprising: detecting edges of items contained in a transmission image of an inspection object in order to produce an edge image; and detecting an item having at least one symmetry property by determining a symmetry line of the items contained in the transmission image, the symmetry line determined by detecting pairs of edge picture elements of the edge image that are positioned symmetrically to each other relative to the symmetry line that is to be determined, wherein, in the determining a symmetry line in the edge image, the only edge picture elements that are taken into account are those for which the symmetry line in the transmission image lies in the image region of the item to which the edge picture elements belong; and producing an output classification associated with the item detected.