Open Access is online access to scholarly research that is free from most copyright and licensing restrictions. This means free access for anyone to read, download, copy, distribute, print, and display.
Governmental Sites can be considered to be public information/public domain, but there may be specific restrictions to use and attribution.
Museums, Galleries, and Libraries may make their content available via public domain, creative commons license, or open access.
Public domain images have no restrictions to use, as in you may alter, change, redistribute, adapt, etc. the image for private or commercial use. No attribution is required for works in the public domain.
Creative Commons Licenses allow for the use, reuse, revision, remixing, and redistributing of images in a variety of ways.
Make sure to review any restrictions for use for each image and abide by any restrictions. Cite the author of each image used.