There is a lot of confusion surrounding the use of material found on the Web. When in doubt there is a good rule of thumb you can use. If you don’t own the item, document, file, track, pic etc. or have written permission to use it you can’t.
That sounds pretty harsh and things aren’t always “black and white.” There is this whole thing called Creative Commons. Essentially defines several types of licenses and rights that an individual can provide to others without surrendering their own copyright protection and ownership.
Within the Creative Commons community are a number of people and sites that publish material that is available for use in creative work. Attached is an in depth description from Professor Trish Anderton at the Cronkite school that will help you in your quest to honor intellectual property.CreativeCommons
Another good resource is “A picture’s Worth 1,000 Links.” This post by Amanda Milligan provides a good guide to finding and citing images.