Google has added a Creative Commons filter to Image Search. In order to use the filter, you'll need to use the Advanced Search option in Google Image Search.
Once on the Advanced Search page, look for the "Usage Rights" option, which is the second from the bottom. You won't see "Creative Commons" listed as an option. Instead, you'll see options for:
- labeled for reuse
- labeled for commercial reuse
- labeled for reuse with modification
- labeled for commercial reuse with modification
Google's not the first to do this. Of course, Flickr has had Creative Commons search for a long time. Yahoo! added a Creative Commons filter to its Image Search last May.
For its part, Google added Creative Commons filtering options to Custom Search plus YouTube began offering Creative Commons licensing this past February. However, YouTube doesn't yet offer Creative Commons search in its Advanced Search yet.