Most images you see online are under copyright, and you should get permission before using them in many situations. Images with a Creative Commons license give users more flexibility.
Creative Commons licenses were developed as an alternative to traditional copyright, allowing creators to choose to allow use of their work under conditions they specify. For example, a Creative Commons license can limit reuse to non-commercial purposes, or to work that also carries the same license. The goal of these licenses is to allow creators more options in how their work is used, while observing current U.S. copyright law.