Reality Check, Unless you file for a formal copyright and or trademark, legally then you are open to the abuse of any public domain material. You must file before releasing it to the public domain. Just slapping a commercial use statement on it or text stateing copyright does not make it so. It is better than nothing but any lawyer worth anything will shoot you full of holes. I have had to deal with these issues many times for professionally produced corporate products, logos, and other materials bothe audio and visual. Once it is out in the public domain and you do not have legal filings, you are on your own.