It is wise to assume everything on the Internet is copyrighted and that to use the material for commercial gain will break copyright law.
Lots of Web sites include a notice giving you permission for the fair use of content, providing you credit your source. If the page gives contact details you can send an e-mail asking permission to use material from a site for a particular purpose if you are in any doubt.
When you publish something on the Internet you should remember that by putting material online you increase the likelihood of it being used by someone else, fairly or otherwise.
