Well, based on what has been said, you could obtain a
Creative Commons Deed, which is legally binding (in conjunction with copyright laws). You can for example, choose to allow people to use markup source code freely (you can't prevent this anyway, if you are petty enough to care), but only republish authored works as long as they inform you. You can also restrict the use of any other material on the site to non-commercial reuse or reproduction. State exactly what you would like (there are checkboxes to choose the details of the deed) and it will give you one appropriate to your needs. It's a legalese-generating extravaganza!
Now even before applying a license like this, some of your site's rights are automatically reserved. News publishing or posting images for example, are not necessarily automatically public domain. Technically, there is no reverse-onus (that is onus on you, the publisher, to get some kind of license) with regard to restriction of such materials' reproduction. The problem with this assertion is its legal enforceability is questionable, because its a very grey area, and because there's really no precedent for, say, a blogger coming out and saying, "you bit my stuff, pay me!"
Which is why Creative Commons exists. Hope that helps.