unfortunately content gets flagged easily when a bot discovers plagiarism. And this just looked like a first indicator. Therefore it is always a good idea to refer to the sources of material (texts, videos, images, etc.) from other websites or your own website at the bottom of each posting.
In this article you see why: https://steemit.com/steem-help/@steemcleaners/why-cite-sources
And in this article you see an example for pictures:
https://steemit.com/steemit/@jokster/how-to-cite-your-sources