Two different ideas
The public domain is a legal status: copyright does not restrict use of the work. CC0 is a legal instrument a rights holder uses to place a work as close as possible to that status.
CC0 and the Public Domain Mark
CC0 is applied by a person who controls rights. The Creative Commons Public Domain Mark is a label for a work believed to be free of known copyright restrictions; it is not a license or waiver.
How to choose
Use CC0 only for work whose relevant rights you control. Use the Public Domain Mark only after careful rights research. If you are reusing a work, preserve the source record and check the item-level rights statement.
Put it into practice
Check your planned use
Select the exact license and use case to open a permanent result page.
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