An often overlooked area of revenue by digital artists is stock image sales. There are many stock image platforms including iStock, Shutterstock and Adobe Stock. These platforms offer a commission each time your image is downloaded by a customer and to increase revenue the licensing agreements usually allow for the distribution of your work across multiple providers.
Each provider has a toolset to submit and track usage of assets. Although there is undoubtedly competition between artists on these platforms, revenue can be significant for popular images. Shutterstock, for instance has paid out over $1 billion to artists since its inception.