There's like 12 Mona Lisa's xP. All of them identical but made from different artists since the original. But yeah, that is a very obvious ripoff of the original artist right there. The artist you're paying for "original" content is not giving original content, which would only hurt your project and you in the long run, especially if you've been paying them for almost all of your art assets. That's not a real artist in my eyes...that's just someone who lacks creativity and isn't deserving of payments anywhere near that high.
What could be done to make such an image different even with the same pose? Simply put, change the background, color of the orc, change what he's wielding from a rock to something like a hammer or an axe, and make enough changes to his face so that is actually looks original and unrelated. Sure, it might be obvious where you got the pose, but since it is now adapted to your own means, this would be original content. A good artist can take any reference and adapt it, and if they're being paid $2000 lol they better know the basics of how to do something like that if they want to use other people's work as a reference.
But yeah, people try to rip devs off all the time with things like that sadly. Especially when it comes to new devs, who might not be aware of where that content came from originally until they start getting heat from players who notice it. Not the type of attention you want on a project lol if you want that project to survive day 1.