The Public Domain Sherpa has an excellent guide to copyright law basics, information about “public domain” works, and a copyright term calculator. But what I really found to be excellent was the “Copyfraud” page highlighting various ways content publishers often make false and misleading copyright claims.
The standard position of many publishers has become “we own everything, and any use we don’t approve of is illegal.”
But all too often they don’t own everything (or anything, for that matter, if work is in the public domain) and you are free under the law to make certain unauthorized and unapproved uses.
False copyright claims made through misleading copyright notices and exaggerated copyright warnings are, basically, copyright abuse. And once you start looking, you’ll see it everywhere.
Check it out.