I've just changed the licence my blogs are published under. Everything that's published in most of the world is automatically covered by copyright and by default the author has all rights to their words (or images) and also by default nobody else has the right to republish the work. Some people choose to allow others to republish their works with or without modifications and there are a number of licences that give these permissions, they are all based in and depend on copyright law.
If you are going to use a free licence you need to carefully choose one that allows your work to be used in the way that you are happy with while blocking uses you consider inappropriate. "Carefully" both to give effect to your wishes and because all the free licences I'm aware of are perpetual and once you've licenced someone to use your work they can continue using it under that licence for the life of the copyright.