Use The Commons search feature to limit your search results to the image collections of cultural institutions like museums and libraries; images use the licensed as having "no known copyright restrictions." Read more about the rights statement here. Make sure to select "The Commons" from the drop-down menu in the search box.
By using Google's Advanced Search feature, you can conduct a Google Images search that will limit your results to only those images that carry a label for reuse.
Types of reusable content includes images that are labeled with a Creative Commons license, images that are labeled public domain, and items labeled with a GNU Free Documentation license. Note that as these designations all differ--from the public domain to the varying degrees of restriction provided for through Creative Commons licensing--it is important to review the license attached to the image before you make use of it.
To limit your results, select "Only images labeled for reuse" unter the Usage Rights feature of the Advanced Search.
Depending on your needs, you may also decide to further customize your search. For example, you may choose to limit your results to only images that are labeled for "Commercial Reuse with Modification." Read more about the Usage Rights search options.
All images need to be cited within the context of the work or presentation (website, paper, project, etc.). Different style guides require different information. Below is a list of what might be needed to cite an image: