Once you understand the protections and exceptions on intellectual property you can begin to search for content that you can use in a legal and ethical fashion. The links provided on this page is not a comprehensive list, but a great starting place for finding reusable resources for your creations.
If you prefer a google search, you can do an image search and limit by license type. You can do this by going to images.google.com and conducting a search. Once you are on the results screen, you need to click the "Tools" link to access additional filters. The filters show up on the page after the subject suggestions. Click on "Usage rights" and you can select "Creative Commons licenses". Always double check the license on the site you visit.