A license guarantees that an image can be used under certain terms for a price. The price of an image depends on a variety of factors including usage purposes, and image size/placements, how long the image is needs for reuse, and exclusivity of the image's use. Regarding "purposes,"
Nwachukwu Works observes four usage categories to start determining image use prices: personal, royalty-free, editorial, and commercial. Many of the wire service images are listed as "Editorial Use Only," but may be eligible for alternative licensing depending on the purpose and proper permission.
Personal Use
Private use with no intent of monetary gain or benefit for the end usage. Price depends on scope of the project and use.
Royalty-Free
Pay once and use the image(s) multiple times without paying additional fees for ongoing use of the work. Flexible usage range, but initial cost can be more expensive due to broad range of copyright coverage.
Editorial
Using images to inform, educate, entertain and comment/criticize. These images are typically used in articles and other educational text, and are priced for usage over an agreed period of time.
Commercial
Using images to promote/endorse something, market/sell products or raise funds. Typically more expensive due to model and property releases, as well as scope of project and audience.