The difference between royalty free and free is that free images do not include any fee to use, but royalty free images simply means a person has rights to use an image without paying ongoing royalty fees. It is a standard licensing agreement in the stock photography industry. Some stock photo sites offer royalty free images , but some come with a one-time fee. Free images may require credit to the owner or must meet other qualifications for use. In addition some sites provide images which have been made through a cc0 license by their creators which are available to use by anyone, however they like.