The royalties section has a very specific language about royalties that makes me wonder if stock photography really falls under that category: "A royalty is a payment, typically based on the number of units sold, by a producer of minerals, oil, natural gas, and other natural resources, to the owner of the site or to the owner of the rights of the property being extracted. For example, royalty income received for the production of oil is measured on the number of barrels sold.".
