Credo Reference is a general reference resource containing reference entries in a wide variety of dictionaries, thesauri, encyclopaedias, quotations and atlases.
JSTOR offers entire collections of back issues of academic journals, together with books, images, and primary sources. Journal coverage begins with the first published issue and ends with a variable date, generally three to six years from present.
Public domain images are images, including photos, clip arts, and vectors, whose copyright has expired or never existed.These images can be used for free by everyone without the need of attributing them, and they can be used for both personal and commercial uses.
This video from CreativeCommons.org offers an overview of the Creative Commons licenses:
If you cannot find images in the public domain, you can use Creative Commons licensed materials.
The following sources make finding images under CC licenses quick and easy. They all have advanced search options that limit the results to images with a specific CC license.
"Creative Commons Licenses Infographic" by ricardo56 is licensed under CC BY-SA