In scientific articles and textbooks I've found the following images (seen at end of this post). These images were created by different authors at different times. The images all describe the same thing/process, the experimental setup one would use to flow a fluid through a cylinder of rock. In each instance where these images (figures) were given the author gave no citation/credit to any of the other authors who gave the similar images in the years prior. For this post's question, let us assume that all of these images are copyrighted and that none of the authors received express permission from the copyright owner of the images that precedes theirs. Here are the questions I would like addressed directly:
What are the objective and/or subjective rules for when an image is considered an outright recreation of another image (and therefore subject to copyright law)? (Citations of these rules would be appreciated)
And per these rules (from question 1), which of the images given below are subject to copyright violation since they are outright recreations? For example, would Figure 4 be an outright recreation of Figure 2, and why?
What figures, if any, are not outright recreations of the others, and why?