The easiest way to add a CC license to your work online is to use one of the tools they provide.
To release your own work into the public domain, Choose CC0
as I have done with Will Bellringer’s mug shot. Had anyone thought to apply copyright to such a thing in 1908, as a government work it would have fallen under Crown Copyright, which lasts for 50 years. So the mugshot unquestionably falls in the Public domain anywhere in the world. There is some question about copyright as it pertains to photographs of public domain works. I myself believe such photographs should never be locked into a second copyright term, so I always release my own pgotographs of public domain images into the public domain, and this tool makes it easy to do.
The catch is that you have to be able to (and know how to) access the HTML
To the extent possible under law, Laurel L. Russwurm has waived all copyright and related or neighboring rights to Will Bellringer’s mug shot.