So, if you have to pay what is "Royalty Free?"
Most Royalty Free galleries provide a license to use their images, which is not the same as purchasing the image.
A royalty is payment to the holder of a patent or copyright or other intellectual property resource for using their property. Royalties are paid per each instance of use. For instance, each time your cable station runs a television rerun, chances are that the station must pay the producer for that presentation.
The bottom line: Royalty Free is not Really Free.