Aw...so in general on Steemit, it is frowned upon to post someone else's work without credit AND permission. If the photographer prefers to stay anonymous, I'd recommend you edit your post to "credit" the anonymous photographer and stating that you have permission to use the image. In fact, without proper credit and permission, it is illegal in most of the world to use someone else's intellectual (creative) work.

https://steemit.com/steem-help/@mindover/don-t-plagiarize-images-here-are-13-free-and-legal-ways-to-find-high-quality-photos-you-can-use-on-steemit