Rule No. 3 of my contest clearly state that only original photos (means taken by you personally) could be used.
In general, if you do use photos from stocks (https://unsplash.com/photos/a-city-street-filled-with-lots-of-tall-buildings-AXviWd0cMGY) you must indicate source, otherwise it is considered as PLAGIARISM and not tolerated in WOX

This is first warning