PLAGIARISM

I have a question regarding plagiarism. I'm about to join an art contest themed "perspective" and I had these idea of a painting but i just can't seem to find the right reference for a posing that ineeded so I browse through pinterest and found a posing anatomy sketch by robert liberace that fits perfectly to may concept idea. I'm not just going to copy the sketch itself and paint it I'm just going to make the sketch as a reference for the posing that I needed. Will it be considered as plagiarism?