Google Advanced Search Tools: Advanced features in Google search engine.
Search Tip: Be sure to select type of search (i.e. Web, Images, News, Maps, Videos). Choose the filters you want to use by selecting the search tools.

Google Image Search: In images, select Search Tools and Usage Rights. Select Labeled for Reuse or Labeled for Non-commercial Reuse to find copyright free images.

Creative Commons Search: Cross-searches multiple sources.
Search Tip: Use the check boxes to refine your search. Use the tabs on the results page to look at various sources and options