What pictures on the internet can I freely copy and use?
My favorite place to find free pictures is from Wikipedia Commons: http://commons.wikimedia.org/ Find the picture or media you want, and read the "permissions".
Also do a search on "CopyLeft", which is a play on the word "copyright".(http://en.wikipedia.org/wiki/Copyleft),
"Flickr" is a site where people can upload their own photos. They have an option to flag them as "copyleft".
So in photos there, that are flagged with "CopyLeft", are available for you. I have included a picture of the CopyLeft symbol below. It's basically a the letter "C" backwards, drawn in a circle.
I use these types of free pictures in the tutorials that I created. I would suggest staying away from all our pictures, unless you are willing to pay a small fee for a "royalty free" or "stock photo". Any picture on a "normal" website, cannot be used without that website's permission (unless they have expressly granted permission). Although it maybe unlikely that you would be sued, the fines and penalties for using a picture without permission could potentially be very steep.
Also - don't get mixed up between "CopyRight" and "CopyWrite". Copywriting is the process of writing good text, typically for a sales letter or advertising. Copyright is the process of legally protecting any work you have written.
I took a copyright class in law school back in the 1980s, but things have changed a lot since then. I have yet to study in much detail the new Digital "Millennium Copyright Act (DMCA)", passed by congress in 1996. See this Wikopedia article for more details: http://en.wikipedia.org/wiki/DMCA