if you want to release images as public domain, you might also wish to release them with a CC0 license since I have heard (but don’t know any specific examples)

if you want to release images as public domain, you might also wish to release them with a CC0 license since I have heard (but don’t know any specific examples) that there are some situations/legal jurisdictions where use of a public domain asset might be unacceptable, but a clear license mostly equivalent to the public domain is acceptable