Well the way that we are setting this up, requires the art to be commissioned and generated (by a trusted artist, who is a part of the project) for a specific purpose. IE it is an original piece of work. Now in this context whether or not a part of that work is not usable is on the artist. The legal ramifications are not on steemstem. Additionally, even here we are not just accepting any user's work, unless said work was already published elsewhere under an open access license of course!
For a photograph, that is a bit more difficult. Its really hard for us to prove that someone took it them-self. It would be pretty easy to find some obscure photos online and post them as original work.
I am likely being overly paranoid.
I am more more paranoid that you ... I am ready to have a wrestling/boxing fight with you and prove that if needed :-D