It should be noted that even though you don't directly copy the assets it's still possible for the copyright holder to threaten with legal actions if they feel their property is being violated, even if the subject is only copying their style or uses a similar image (like yours), if they do take that threat to court the outcome is usually dependant on who has the most expensive(best) lawyers and how derivative is the subject of copyright violation. It happens all the time, it's called copyright trolling/trademark trolling. One famous example is The Banner Saga that got legal threats from King for using the word 'Saga' in their title.
The bad thing about legal trolling like this is that they usually go after smaller companies or individuals who don't have the money to pay legal fees and even if no legal actions are taken most of the time the threat is scary enough to force the accused to change their work, because you never know, they might actually take it to court. So they are rather safe than sorry. It's all about protecting their products, even if they do it through questionable methods.
Just ought to let you know.