Anyone has copyrights to anything they create, as soon as they create it. No need to register or mark it in any way, however that's usually a good idea if it can be done easily. Check out my blog post http://www.theresasheridan.com/blog/the-copyright-mystery/
Put a copyright clause on the bottom of your sight or blog. There are scripts that you can use to block right-clicking, but they're kind of a pain, and while they work in websites, I don't know if they'll work on blogs. Maybe there's a plug in or something more user friendly for blogs.
And yes, put up low resolution images, because they won't be very suitable for printing, if that's what someone wants them for.