CC0, CC Public Domain
totally free
Public domain
The public domain (PD) consists of all the creative work to which no exclusive intellectual property rights apply. Those rights may have expired, been forfeited, expressly waived, or may be inapplicable. Because no one holds the exclusive rights, anyone can legally use or reference those works without permission.
https://en.wikipedia.org/wiki/Public_domain

Seonglae Cho