Who specifically is saying it is not free for use? The author said it is public domain and free for public use, and quote, "Giving credit to the photo author or PIXNIO is not required". Nothing was plagiarized. If you wish my post was longer that's one thing, but making a plagiarism claim is another.

Author: Rosendahl https://pixnio.com/flora-plants/bushes-and-shrubs/lingonberries-with-green-leaves