When it comes to stock photography, there can be some confusion between “Rights-Managed” images and “Royalty-Free” images, as each one has a different model for pricing and usage.
For the record, the basics:
Rights-Managed images are “rented” for a specific purpose at a specific price. The cost is based on usage. Generally, the fee charged is based upon the scope of the project, and the permission to use the picture will be limited to that which is outlined on the invoice.
Royalty-Free images are purchased outright, either as single images or on disc volumes in bulk, and can be used any way you want, with certain restrictions. They’re most often priced based upon digital file size, and have no concern with how you are actually going to use the images.