Is it allowed to post none commercial licensed artwork in the screenshots I post on social media before the game is released, or even in very early state? It's not intentional marketing but marketing none the less. I use a lot of place holders for my games and like to sent out a occasional tweet, blog, update, etc. I don't think this is allowed so I refrain from doing so but reaching out to the public helps me focus on my project more.

I know asking the artist is always good but for a lot of free art there is no contact information. Like the re-seller sites which offer free items as well. So what are the rules here?

Well, I guess that was a stupid question now I think about it. For what it's worth, I am not posting anything into the world but I guess that does not matter since it's still a commercial project and some of the artwork is licensed NC.

The thing is, I want get the look and feel of the game right by picking whatever I can find before I'm going to make any artwork myself because that is taking ages for me. I'll guess I have to replace it with what I have and can find that can be used for commercial projects.

Have you tried seeing who owns the artwork your using and asking them if you would be allowed to show them off in a non release version of the game only included in screenshots. They may say yes, never hurts to ask.

Yeah, that is the best way to go. But sometimes people release work for free on re-selling sites like turbosquid and they don't give contact info obviously. Already started creating my own tile-set since I really want to open to the public with my current project.

Best thing is to ask permission.

I once contacted a former team leader for permission to use his 3D art as a placeholder for a Kickstarter campaign. He agreed, as long as I replace the art for the final product.