Miha, my experience with the clips is that they do not punch holes. They must made a mark of some kind of course. If they didn't then thye would not hold the paper but all I can say is that the marks they make are either so small as to be invisible or the paper somehow loses the marks within a very short time. When I look at the prints again within a few hours I am not conscious of the marks, nor has anyone else who looks at the prints ever mentioned seeing any marks