I'm not sure I understand the scope of your question? But I assume you mean how can you tell if files are copyrighted or not.

Well, if you personally ripped the mp3s yourself and you own the CDs then you know that all of the files are copyrighted. However if you are asking how can someone else tell if the mp3s on your computer are copyrighted or not. Let me put it this way, The problem isn't whether they are copyrighted or not as most material IS. The question is whether you are sharing this material with other people (over the Internet mainly that causes the problem.) So in essence it doesn't matter if you bought the CD. By sharing you are infringing on someones right to distribution as you did not obtain permission to do so.

Hope this help.

http://www.leeware.com