Many authors let you use their work freely without permission based on certain conditions. Creative Commons licenses provide a flexible range of protections and freedoms for authors, artists, and educators to offer a voluntary “some rights reserved” approach.
This search engine helps you quickly find those authors and the work they have marked as free to use with only “some rights reserved.” If you respect the rights they have reserved (which will be clearly marked, as you’ll see) then you can use the work without having to contact them and ask. In some cases, you may even find work in the public domain — that is, free for any use with “no rights reserved.”
“This search engine identifies websites that either contain metadata of or a link back to a Creative Commons license. By returning these search results, we are not making any representation that the linked content is actually or is lawfully offered under a Creative Commons license. You must independently verify the terms under which the content is made available and make your own assessment as to whether these terms are lawfully applied to the content.”
You can choose to find works usable for commercial purposes or those you can modify, adapt, or build upon. You can limit your search using Google, Yahoo and Flickr. Also try searching through their featured directories of licensed works.