Quote is your friend. Just post the link or author/photographer of whatever you are posting. That way you're not passing off someone else' photography or article as your own. Most people are happy with this as it increases publicity for them, those that are not happy, if that ever happens, then they will first ask to remove the picture/article before any further action is taken, but this is extreme cases.
also if you use the tags then your just linking to their picture, rather than downloading and then uploading on the RB server.