Copyright
These days almost all major nations follow the Berne copyright convention. In the US, nearly everything created originally and privately is copyrighted, hence protected, regardless of whether it has a notice or not.
To be on the safe side legally as well as morally, operate on the assumption that other people’s works are copyrighted, and may not be copied, unless you know otherwise. Even though on some mostly old stuff copyright protection has expired, be sure you operate on knowledge and not hearsay. It applies to pictures, too.
If it looks copyrighted, it probably is.
Notes:
Creative people before copyright didn’t let the absence of copyright prevent them from being creative. Their music, art, books and thoughts continue to inspire generations, not because they didn’t have copyright back then, but thanks to it.
Where is the copyright craze taking us? Will future Jack Nicklauses swing copyrighted golf swings, future Federers hit copyrighted passing shots, future Peles score copyrighted goals?
I’m in favor of protecting intellectual property, but the thought of simply feeding the scarcity mentality – and lining lawyers’ pockets – I do not find attractive.
My mantra: if you must steal, don’t let copyright stop you. If you must plagiarize you might hurt others and in the process gain benefit for yourself, but in the long run you’ll only hurt yourself the most.