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plagiarism is taking the work of others and passing it as your own without crediting the authors. In this case the photographer created his work of art/composition, your work is completely based on the work of art of the photographer, a derivative work, and you dont credit the author, hence, its plagiarism.
Additionally, you dont have permission to monetize derivative works of that copyrighted photograph, so you are also infringing copyright law.

There are many ways of borrowing, in which there is nothing bad, and resorted to by the most eminent masters.

Borrowing implies consent, you do not have the consent of the author of the photograph.

Plagiarism is an appropriation! I have not appropriated photos of the author! I painted a portrait!

Go ahead and learn more about art plagiarism here: https://steemit.com/abuse/@jaguar.force/what-is-art-plagiarism-by-francis-leverett-golden inform yourself about the true scope and shades of art plagiarism.

Plagiarism is not only taking someones drawing/photograph/artwork and passing it as your own, thats called art theft, and its only the most blatant form of art plagiarism, the most common one is called art paraphrasing, which is what you are doing.

If somebody gives you a picture so you make a portrait of them, thats a different thing, since they are the model on the photograph and have the right to use it.

In this case, the photograph is Copyrighted by the photographer, that means that the photographer reserves all the rights of the picture to herself, and that means that to make derivative works of that photograph, as for example Your Drawing, you need permission from the author to do so. Additionally since by posting it in Steemit you are monetizing it you also need permission from the author to do that as well.