Can I post an article on Facebook? How do I know if an article, book, or photograph is under copyright?
The Office of Copyright under the auspices of the Library of Congress publishes "Copyright Basics" which will introduce you to "intellectual property" laws and regulations. The "fair use" provisions of the law are complex and it is essential to understand the restrictions prior to "posting" or distributing material that is under copyright.
Here is a summary from the Copyright Office:
"The safest course is always to get permission from the copyright owner before using copyrighted material. The Copyright Office cannot give this permission.
When it is impracticable to obtain permission, use of copyrighted material should be avoided unless the doctrine of fair use would clearly apply to the situation. ... If there is any doubt, it is advisable to consult an attorney."