I have some standard advice that I give to quiz writers about how to avoid this type of unintentional plagiarism.

The first is to take your research notes with a paper and pen. Don't use any kind of copy and paste function. If you are taking paper notes, you are not likely to use the wording of the source, but instead to jot down something like "1939 Atlanta Vivien Leigh". You've given the wording used by your source less of a chance to cement itself into your brain.
Second, use more than one site for research. Besides the obvious benefit of this confirming your answer, seeing the same information presented in more than one fashion keeps any particular wording from "taking", quite as much.
By the way, if you find that all of your sources use exactly the same wording, you will know that they have been plagiarizing each other. This means that you have not, in fact, confirmed your answer with more than one source - it's all the same source, even if it's fifteen different websites. This accounts for the way you will sometimes be accused of plagiarism from a website that you've never even visited - it just happens to be the one the editors found your wording on.
Third, wait a few days after researching before writing up your quiz. The turns of phrase used by your source will have a chance to fade from your mind.

We understand that in the bald stating of facts, it's pretty easy to use exactly the same wording as someone else. There are only so many ways to say "Ernest Hemingway was awarded the Nobel Prize for Literature in 1956". For the most part, your editor won't even mention that kind of coincidental wording. What we tend to see most often, however, is something like "Hemingway - himself a great sportsman - liked to portray soldiers, hunters, bullfighters - tough, at times primitive people whose courage and honesty are set against the brutal ways of modern society, and who in this confrontation lose hope and faith." It's no coincidence that this wording is exactly the same as used on http://nobelprize.org/nobel_prizes/literature/laureates/1954/hemingway-bio.html .
I think you can understand the editors' rather jaded response to protests of innocence when we see this sort of thing.

Those are my sentiments exactly. I just try to give ways of avoiding it to people and major benefit of the doubt.
I personally use the handwritten method on a sheet of graph paper for some reason.
I'll force myself to jot down notes on that...then compose the questions. I'll write down ten items I want to write about as I research. Like amethyst, ship of same name, meaning of name, mine in Finland, goblet, Moh's scale, and then I come up with the questions. Sometimes I check my own work in Google! Not that I doubt myself, but, it could conceivably be too close to the source without me knowing it.

It isn't easy to broach the topic of plagiarism, but, if someone is willing to accept that their method has led them astray, then, we can work it out. Or, if they have some valid reason like being the author of an article or book on that topic.
I ask people to tell me which sources they used when I'm uncertain, and most people are willing to do so.

Again, I believe plagiarism.org is a useful cite if you want to know more about what plagiarism is and how to avoid it.

I wonder if there's some confusion here. There are really two issues here.

Put simply:

Plagiarism is the use of material (text or images, etc.) as if one had created the text, etc. oneself - in other words, without acknowledgement. There may or may not also be a breach of copyright involved. (Some texts are no longer copyright, for example).

Breach (infringement, violation) of copyright is the reproduction, without permission, of material protected by copyright. (Sometimes there may be agreed procedures for the reproduction of certain kinds of copyright material).

Though often related, the two issues are separate.

Please note that I'm not a lawyer and the above is simplified.

If you had this sentence that appeared on twenty sites:
"Swiss cheese or Gruyere has holes", it wouldn't be plagiarism.

If you had this one: "The ever enduring cheese treat "fromage Gruyere" hails from the Swiss alps and as everyone knows, has cute little holes tunneling through it giving it its cachet".


When I've looked up people's sources on food quizzes sometimes, I'll get about ten sites that are using each distinctive text like the latter example, and frankly, it's hard to tell who copied from whom, nor does it matter. We don't want that text on our quizzes.

Ah, Bloomsby! I believe you are correct.

That's true - our definition of plagiarism on this site is not the legal one. When an editor uses the word "plagiarism" on this site, we usually are referring to our site's policies regarding copying.

What I should have said, above, is "you will know that they have been copying from each other."

This is going to sound kind of dumb, but where would you find a green screen if you had one?

It would come up on your edit screen - a message about three or four inches high right at the top, on a green background.