Fair use is determined on a case-by-case basis. Intention is one of the considerations, so users should make the initial assessment. There are four factors that courts use to determine fair use in the US:
Cornell University maintains a checklist to help people determine whether their proposed use falls under fair use.
If the type of use you're considering does not fall under fair use and the work is not in the public domain, you will need the copyright holder's permission.
You should always attribute and cite an original work, but you will also need a license. Although licenses can be written, spoken, or implied, it is safest to get permission in writing. Depending on your proposed use, you may need to consult legal counsel.
More information about licensing a work.
Copyright is not absolute. "Fair use" grants legal exemptions to the exclusive rights of copyright holders under certain circumstances. This means that portions of a work can be used, even if the work is in copyright and without permission of the copyright holder, as long as specific guidelines are followed. This LibGuide deals with fair use in the United States, as that is where Oberlin College is located.
In general, fair use favors educational, transformative, and nonprofit use of items in copyright. It also takes the nature of the copyrighted material into consideration and evaluates the proportion of a work to be used or adapted.
Content derived from: Checklist for Conducting a Fair Use Analysis Before Using Copyrighted Materials and Copyright Services: Fair Use by Cornell University Library. CC BY 4.0.