These images are owned by organizations that specifically allow them to be used without permission and without any charge for specific purposes (for which SUNY Empire courses qualify.)
Creative Commons images are not in the public domain. They are published with a license that specifies what you can do with them. You are allowed to use them without permission and without any charge, but you must follow other specified restrictions, which are explained here:: http://creativecommons.org/licenses/
Be careful of using any work with ShareAlike license, because often we cannot abide by its requirements. Faculty contracts and SUNY rules stipulate that faculty retain copyright to the courses they create, and that would violate the ShareAlike license. It's ok for things made by students and professional staff as long as you put a CC ShareAlike license on it.