Google Image Search added an option to restrict the search results to Creative Commons-licensed images, that allow content creators to share their works with the world. The options aren't yet available in the interface, but you can customize searches for combination of licenses, just replace the last part “cc_publicdomain” with you choice. Here’re some examples: public domain images, images licensed using Creative Commons Attribution, images licensed using Creative Commons Attribution Share-Alike, Reuse, Commercial reuse, Reuse with modification, Commercial reuse with modification.

Source:→ Google OS