When is an image considered a recreation of another image?

Question

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:

1. 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)

2. 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?

3. What figures, if any, are not outright recreations of the others, and why?

Answer 1

An image is a copy of another image or a work derived from another image if it was created by copying the other image or by copying the other image and then modifying it.

If you are in court for copyright infringement, then the accuser has to prove their claim. If you have 1,000 lines of code identical to 1,000 lines of code that I wrote a year earlier, then it is so unlikely that you created the identical code by coincidence that a court will assume you copied.

If you have two identical or very similar looking images, then if these images depict some facts of nature, then anyone creating that kind of image would end up with very similar images. Or if several photographers take photos of the Eiffel Tower, those images will look similar. So a court will take the situation into account to decide if similarity is proof of copying. Having access to the originals may be an indication of copying.

(Looking at the tiny lines in the background pattern which are in identical positions, I think the creator of image 5 would have a valid claim against image 6. Image 3 vs 4 I would leave it to the lawyers and the judge).