In getting permission, it is important to understand the crucial distinction between “Copyright Permissions” and “Use Permissions.”
The copyright for a work (a painting, a sculpture, a drawing) is not necessarily held by the owner of the physical work; in fact, in most cases the owner of the work does NOT own the copyright. For example, you wish to reproduce Picasso’s The Old Guitarist, found in the collection of the Art Institute of Chicago. You request a reproduction from the Museum, and they provide a high-resolution digital file, along with non-exclusive world rights to reproduce this image in your publication. But all that the museum has granted is the USE of their reproduction; you must still obtain permission to publish the underlying work from the owner of the copyright, the Picasso Estate (administered in this case by Artist Rights Society-ARS).
Some older works are in the Public Domain, which is to say that they are no longer in copyright. Laws vary from country to country, but the safest way to determine if a work is in the Public Domain is this: date of the Author/Artist’s death plus 70 years. To use our previous example, Picasso’s works will enter the Public Domain in 2043.
If you want to use someone else's work, you often need to get permission from the author or creator of the work. Even though technology has made information more accessible to everyone, copyright and trademark laws still apply to online.
Here are some tips that can help you avoid legal trouble when using other people's work:
Assume Others' Work Is Protected - You may not freely use someone else's work simply because it has been posted on the Internet (a popular fallacy). Whether you find the material online or off, permission is generally needed to reproduce text, artwork, photos, and music. It is wise to operate under the assumption that all material is protected by either copyright or trademark law unless you have good reason to know that it is not.
Using copyrighted work. As a general rule, any original work -- whether text, visual art, photos, or music -- is protected by copyright law, which means that you may not reproduce it without permission from the copyright owner. Giving credit or thanks to the copyright owner does not change that; you are not allowed to reprint (or distribute, adapt, perform, or sell) the work without the owner's authorization.
Using trademarks. Similarly, if your site sells products or services, permission is often needed to reproduce a trademark, including any word or symbol that identifies and distinguishes a product or service from others -- such as the word "McDonald's," the distinctive yellow arches, or the Ronald McDonald character.
Copyright or trademark infringement. Reproducing someone's copyrighted work or trademark without their permission is known as infringement, and it leaves you vulnerable to lawsuits from the copyright or trademark owner. Lawsuits are even more likely if you stand to make any money off the use.
Read Click-Wrap Agreements - Many companies offer artwork, photos, and other materials for reuse -- alternately called clip art, royalty-free work, copyright-free work, shareware, or freeware. Do not assume that these materials can be distributed or copied without limitation. To be certain that your intended use is permitted, read the terms and conditions in the "click to accept" agreement or "read me" files that usually accompany such materials.
When In Doubt, Seek Permission - Getting explicit permission from the copyright owner is the best way to avoid a lawsuit. Some sort of written consent (even an email) is preferable because it will be easier to prove if a dispute arises.
These sites provide in-depth information on requesting copyright permission.