If a particular material is under copyright, it does not necessarily mean that no one else can use it. It generally means that someone else has to gain permission from the copyright owner before using it. The owner of a copyright can, of course, choose to withhold permission, which can limit the other party's ability to use it legally.
According to Stanford University, there are two types of permissions that a person can gain to use copyrighted material. One is a release, which protects the borrower of the material from lawsuits related to its use. The other is a license, which gives the borrower the right to use the material. There may be some overlap between the language of a release and a license. Therefore, the title of the document is less important than the terms of the agreement.
The U.S. Copyright Office explains that there are a few situations in which it is not necessary to obtain permission from the copyright holder before using a work. Public domain works have copyrights that have either expired or are otherwise invalid. There is no need to obtain permission before using a work that is in the public domain. A borrower may also make use of limited portions of a work for purposes of scholarship, news reporting, commentary or criticism under the principle of fair use. However, the circumstances dictate whether the use is fair or not, so when in doubt, it is best to ask permission of the copyright holder.
A borrower who does not know who owns the copyright to a work can contact the Copyright Office, which can provide whatever information is available in the records upon request.