It's a FREE IMAGE that can be used in the "design concept"..what's your problem? I can do an edition to that image if the contest holder requested.
Here's the changes, thank you for choosing my design concept... i made a new "man image" if you like a customized one. But, still u can choose the "prior image" it's free to use.
It is a copy of someone's artwork, not your own. You do not know if it is free or not, just because it was not on Shutterstock, as the other post had, does not make it free. You are selling something that is not yours. The rules state that you are not to copy. Own up to it.