I would like an option that will allow me to put an image into the public domain, such as Creative Commons’ CC0. This is important especially if I’ve taken an image from the public domain and modified and used it. I don’t want to put a copyright even with a permissive license such as CC BY on it because that is more restrictive than the original.
From their website
Use this universal tool if you are a holder of copyright or database rights and you wish to waive all your interests, if any, in your work worldwide. This may be the case if you are reproducing an underlying work that is in the public domain and want to communicate that you claim no copyright in your digital copy where copyright law may grant protection.”