Here is a quite interesting post: 5 Steps to Prove You’ve Been Plagiarized
If there’s one thing that I’ve learned over the past 13 years of running Plagiarism Today, it’s that a LOT of people think they’ve been the victim of plagiarism.
However, those who are right and can prove it are the exception to the rule. … proving you are a victim of plagiarism, enough to convince a court of law, is extremely difficult. So, before you either hurl accusations or, worse yet, file a lawsuit, it makes sense to see if you can actually prove your case.
1. Prove your idea was original. The author of this post, Jonathan Bailey, says this is no problem with verbatim text but next to impossible for ideas. That certainly sounds right to me.
2. Show that what was copied could be protected. Here Bailey means that ideas are not protectable under copyright law, although the exact expression of those ideas is. This makes sense as well.
3. Show the plagiarist had access. That certainly seems necessary.
4. Show that the plagiarized work is sufficiently similar to your work to establish it was stolen. There’s where most important judgment calls would be made, I expect. Bailey says that strings of twelve identical words can be sufficient to establish that the derivative work was copied from yours.
5. Prove the copied material lacks attribution. Well, that immediately seems silly, but Bailey says, “This might seem silly [my exact response, as you see] as it should seem pretty obvious whether or not a use is attributed, but that isn’t always the case.” Then he gets into incorrect citations in academic papers, which, sure, I get that this can be a problem, but it wasn’t what I was really thinking of as plagiarism.
The bottom line:
Because of this, it’s important to not ask “Did plagiarism take place?” and instead ask “What plagiarism can we prove?” When we look too long and hard at plagiarism percentages or word counts, we often miss the more important questions about plagiarism…While being a victim of plagiarism can be costly (both emotionally and practically), it’s not nearly as costly as making allegations that the evidence does not support.