First off! I'm not now nor have ever been a lawyer and I have never worked as an expert on Copyright Law.

Note: This post is for general informational purposes only, and not to be considered legal advice. If you have specific legal questions about a marketing campaign, you should speak to your attorney. The information herein is a summary of an article by Molly Siems, Director of Legal and Business Affairs at NewsCred that originally appeared on WIRED.

• The Copyright symbol is not necessary. Copyright attaches as soon as it is "fixed," i.e. set to paper, typed, recorded, etc.
• Authors do not have a total monopoly on their work through "fair use." This allows limited use of a copyrighted work for criticism, comment, news reporting, teaching, scholarship or research.
• Watch out for Images, even thumbnails! Be sure the image is in the public domain or you have license to use it. Certain images are in the public domain and can be used without worry. Flickr, for instance, licenses under Creative Commons. BUT,  you may use them only under certain conditions -- READ THE LICENSE.
• Don't Scrape! If you're going to use a bot to find information, SEE A COPYRIGHT LAWYER.
• Think if you're using whole or large parts of an author's work or copyrighted images. Giving full attribution is not enough -- even if you're linking back to the original author -- GET PERMISSION. (In my previous post on Dystopian Fiction, I got the author's okay in an email before I posted it and what I'm posting here is a summary of an article covering over three pages on copyright.)

Attribution has nothing to do with Copyright Law -- it helps you avoid an allegation of plagiarism. You are infringing on an author's copyright by displaying his or her work. Copyright, like all legal matters, gets very involved in fine details. Satisfy yourself that you are using another's work legally.

I hope this answered more questions than it raised.