Instead of starting with a Google image search, why not try one of these websites?
Click for Sarah's list of image websites.
Here are some of my favorites, to get you started:
LIFE magazine photo archive, hosted by Google
Civil War Photos
Historic Photos from the Library of Congress, on flickr
The New York Public Library's Picture Collection
The New York Public Library Digital Gallery (or try the Beta version of the Digital Collections site)
Digital Public Library of America (DPLA)
Additionally,rethink your favorite social media tools like tumblr and Pinterest for collections of themed images. Quality and accessibility will vary but they are great for getting ideas.