There are no restrictions on ideas and thought processes only on intellectual works and productions. But if you conscientiously and deliberately copy someone elses work then you are infringing on copyright laws. So you either know or you dont if you are copying something. So I wouldnt worry if you think youre probably using an idea that might have been used in many variationshow many Bryce sphere images have you seen or Poser Vickies and Michaels? I havent seen many scull head shaped martini olives.