For example, your read an article in your field and you see that some of the content resembles your style and information in a paper you already wrote some time before, is that a 'concealed' plagiarism? I saw that in few chemistry papers.
In my opinion people usually plagiarise pictures, schematics and charts. This is the same unethical behavior as copying text. This is of course result of laziness -
Thank you all for your answers. Now there are more explicit forms of plagiarism. That is worrying indeed. That suggests that the authors should exercise a some sort of effective self-policing to detect and report plagiarism. Plagiarism can get more and more difficult (but probably more concealed, though) to do.