Royalty free (RF) images are licensed once and may be used in multiple projects for an unlimited amount of time. There are some limits to most of the RF licensing agreements, the rights granted are usually very broad. There are some advantages to RF and the potential advantage of the RF sales model is that its simple pricing structure often leads to a significant increase in sales, producing more income for photographers than the RM sales model. While the average RF sale is often lower than the average RM sale, the greater number of RF sales ends up producing a higher overall income for the photographer. (Naturally, this is not always the case, and some unique images should only be marketed under the more controlled Rights Managed and Rights Protected where the highest fees can be obtained for those images.