This type of question occurs frequently and there are numerous threads with large discussions on this topic, but it boils down to a few salient points:
1. As far as I'm aware, no one on here is a lawyer, and therefore cannot give adequate legal advise.
2. If you decide to use graphics that are not your own, then YOU must take responsibility for that action, and any subsequent litigation that could occur because of your actions is then entirely on your shoulders.
3. Any answer you get here will generally be purely speculative and mostly subjective.
4. It will ALWAYS be more preferable to create or 'buy-in' any graphics that you intend to use, especially in a commercial venture.
In summary, the choice is yours.
If your vision so exceeds your ability, then look to something closer.