I'm no expert but here is my ethical opinion. If your work is substatialy different in nature from the elements it was composed of such that those elements are unrecognizable, and those elements were published free of usage restriction than go ahead, though courtesy/moral obligation would be to credit the authors of those elements and provide links to them. If the authors of the elements did not give a complete release from all use restrictions than you must contact them, show them the work, negotiate credit and compensation or remove those elements from your work no ifs,ands,or buts about it.