How can I control how copyright material is used on my blog?

You can certainly control how your copyright material is used. There are many ways to exercise this control, so you should give it some thought and then communicate your policy clearly on your blog. There is no fixed format that a licence or terms and conditions must take.

Some considerations you may have include: Do you want your work to be freely distributed to maximise your reach without bothering about dollars and cents? Or do you want to restrict use to only non-commercial distribution and copying? Will you allow others to modify your work? Under what circumstances?

For some ideas, Creative Commons (CC), a non-profit organisation, offers a range of flexible copyright licenses for creative works. You may even consider adopting one of CCs licences at https://creativecommons.org/about/cclicenses/ .

For comments by readers, you should similarly be clear what are your terms and conditions for comments. If a reader leaves a comment, there is at least an implied licence that she allows her comment to be viewed on your blog. If you intend to use your readers’ comments beyond this, you should clearly state this on your blog.