The following is provided for informational purposes only and should not be construed as legal advice. If you need legal advice, contact a lawyer.
Copyright law protects original creative works, such as software, video games, books, music, images, and videos. Copyright law varies by country. Copyright owners generally have the right to control certain unauthorized uses of their work (including the right to sue people who use their copyrighted work without permission). As a result, certain images and other copyrighted content may require permissions or licenses, especially if you use the work in a commercial setting. For example, even if you have permission to use an image, you may need additional permission to use what is in the image (e.g., a photo of a sculpture, a person, or a logo) because someone else's copyright, trademark, or publicity rights might also be involved. You are responsible for obtaining all of the permissions and licenses necessary to use the content in your specific context.However, even copyright-protected works can be lawfully used without permission from the copyright holder in certain circumstances. The Wikipedia entry on copyright law contains a useful overview of copyright law, including fair use and other exceptions to copyright law.
Of course, some online content is not free to use, is not licensed by the copyright holder, and your use will not qualify as fair use. Unfortunately, we can't provide specific guidance regarding the use of particular content, so be careful to select the works you use carefully.