In our case (Glaze), we are using a simple freemium model. The assets are free to use as long as the user attributes the illustrator and Glaze. If the user wants to buy a license so that they can use the image without crediting the artist/glaze, they can pay for that license (they also get a larger file size and the source file).
Unsplash is a bit different, all of the images are completely free. From my knowledge, this was originally used as a marketing funnel for their parent company, Crew. Crew has since been acquired and Unsplash has spun in to it's own entity. Nowadays my hunch is that they are monetizing through calls to their API (Unsplash is integrated into big players like Squarespace, Trello, Medium). Feel free to fact check as I am no expert when it comes to Unsplash's business model.
Unsplash is a bit different, all of the images are completely free. From my knowledge, this was originally used as a marketing funnel for their parent company, Crew. Crew has since been acquired and Unsplash has spun in to it's own entity. Nowadays my hunch is that they are monetizing through calls to their API (Unsplash is integrated into big players like Squarespace, Trello, Medium). Feel free to fact check as I am no expert when it comes to Unsplash's business model.