Anything protected by the copyright law has a legal concept that grants artists or authors control over their creations. On the other hand, anything in the public domain is not protected by intellectual property laws and the public owns these works.
A book published in 1758 can be classified as belonging to the public domain. According to U.S laws, works or creations published in the U.S before 1924 might be deemed expired.
As a bloggers, when you hit the publish button, any work created is protected by copyright and the material inside is yours.
A music record from the 1960s - protected by copyright law
An infographic made by the federal government - public domain
A photograph taken in 1980 - protected by copyright law